Low-loss magnetic powder core, and switching power supply, active filter, filter, and amplifying device using the same

ABSTRACT

A magnetic powder core comprises a molded article of a mixture of a glassy alloy powder and an insulating material. The glassy alloy comprises Fe and at least one element selected from Al, P, C, Si, and B, and has a texture primarily composed of an amorphous phase. The glassy alloy exhibits a temperature difference ΔT x , which is represented by the equation ΔT x =T x −T g , of at least 20 K in a supercooled liquid, wherein T x  indicates the crystallization temperature and T g  indicates the glass transition temperature. The magnetic core precursor is produced mixing the glassy alloy powder with the insulating material, compacting the mixture to form a magnetic core precursor, and annealing the magnetic core precursor at a temperature in the range between (T g −170) K and T g  K to relieve the internal stress of the magnetic core precursor. The glassy alloy exhibits low coercive force and low core loss.

This application is a divisional application of U.S. application Ser.No. 09/809,366 filed on Mar. 15, 2001 now U.S. Pat. No. 6,594,157,entitled “Low-Loss Magnetic Powder Core, And Switching Power Supply,Active Filter, Filter And Amplifying Device Using The Same”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to magnetic powder cores and to methodsfor making the same. In particular, the present invention relates to alow-coercive-force, low-loss magnetic powder core and a method formaking the same. The present invention also relates to switching powersupplies, various converter circuits, and active filters. Furthermore,the present invention relates to filters and amplifying devices, andparticularly, relates to a low-loss filter outputting less distortedwaveforms.

2. Description of the Related Art

As magnetic cores used in core components, such as transformer cores forswitching power supplies and smoothing choke cores, which require aconstant permeability up to the high frequency region, ferriteclosed-magnetic-circuit cores, ferrite gapped cores, andamorphous-alloy-tape-wound cores provided with gaps have been proposed.Also, magnetic powder cores formed by compacting a mixture of a powder,such as carbonyl iron, permalloy, or sendust, and an insulating materialhave been proposed.

Ferrite sintered magnetic cores exhibit low core loss, butsimultaneously exhibit small saturation magnetic flux densities. Thus,in ferrite closed-magnetic-circuit cores and ferrite gapped cores, aleakage magnetic flux from the gap section adversely affects peripheralelectric circuits. Magnetic powder cores using powders of carbonyl iron,permalloy, and sendust have the disadvantage of large core loss,although the cores exhibit higher saturation magnetic flux densitiescompared to ferrite magnetic cores.

In recent years, development of electronic devices has advanced with anincrease in the use thereof. In particular, the weight of thedevelopment was shifted toward reducing heat dissipation by reducing thesize of the electronic devices and reducing the power loss. In order toachieve these aims, switching power supplies, various DC/DC convertercircuits, and active filters have been improved. These devices usevarious types of magnetic elements having magnetic cores. Ferrite ismainly used for the magnetic cores. In some cases, carbonyl ironmagnetic cores, FeAlSi-alloy magnetic powder cores, and FeNi-alloymagnetic powder cores are also used.

A ferrite magnetic core is generally provided with a gap to preventmagnetic saturation. A leakage magnetic flux from the gap will adverselyaffect peripheral circuits. On the other hand, a NiZn ferrite coreexhibits a large core loss, resulting in high heat dissipation from adevice using this core. A carbonyl magnetic powder core exhibits anextremely large core loss, resulting in significantly high heatdissipation compared to ferrite magnetic cores. In addition, in aFeAlSi-alloy magnetic powder core and a FeNi-alloy magnetic powder core,the core loss thereof is lower than that of the carbonyl iron magneticpowder core, but still does not reach required levels.

Low-pass filters have been used for smoothing the pulse shape outputfrom impulse modulation amplifiers. The requirements for low-passfilters are low loss and less distortion of smoothed waveforms. Alow-pass filter is generally provided with a capacitor and an inductorcomposed of a coil with a magnetic core. Achievement of theserequirements strongly depends on properties of the magnetic coreconstituting the inductor. Thus, conventional low-pass filters useamorphous magnetic cores provided with gaps, ferrite cores provided withgaps, or carbonyl iron gap-free magnetic powder cores.

However, in filters using amorphous magnetic cores provided with gaps orferrite cores provided with gaps, leakage magnetic fields from the gapsmay adversely affect peripheral elements and circuits, resulting indecreased stability in the entire circuits including the filters andgeneration of noise. Moreover, in these filters, the amplitudepermeability varies with changes in the magnetic field and exhibits alarge rate of change. When a pulsed current causing a large change inmagnetic field is smoothed, the waveform will be significantlydistorted.

In the carbonyl iron gap-free magnetic powder cores, the dependence ofthe amplitude permeability on the magnetic field is constant, and thewaveform is not distorted. However, the carbonyl iron gap-free magneticpowder cores dissipate a significant amount of heat due to large coreloss.

The large core loss in conventional magnetic powder cores is due tolarge core loss of the magnetic materials themselves used for themagnetic powder and insufficient relaxation of stress which is appliedduring compacting of the magnetic powder cores.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amagnetic powder core having low coercive force and low core loss and amethod for making the same.

It is another object of the present invention to provide a switchingpower supply, converter circuits, and active filters which exhibit lowheat dissipation and which can be miniaturized.

It is another object of the present invention to provide a filter whichdissipates less heat due to low loss and which suppresses waveformdistortion, and an amplifying device provided with this filter.

According to a first aspect of the present invention, a magnetic powdercore comprises a molded article of a mixture of a glassy alloy powderand an insulating material, the glassy alloy comprising Fe and at leastone element selected from Al, P, C, Si, and B, having a textureprimarily composed of an amorphous phase, and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

Since the magnetic powder core of the present invention comprises amixture of the glassy alloy powder and the insulating material, theinsulating material enhances the resistivity of the entire magneticpowder core. Thus, the magnetic powder core exhibits reduced core lossdue to reduced eddy current loss and high permeability in ahigh-frequency region.

Preferably, the glassy alloy has a resistivity of at least 1.5 μΩ.m. Theeddy current loss in the glassy alloy particles in a high-frequencyregion is thereby effectively decreased, the magnetic powder coreexhibiting further reduced core loss.

The magnetic powder has a coercive force of preferably 80 A/m or lessand more preferably 40 A/m or less in an applied magnetic field of ±2.4kA/m.

Preferably, the magnetic powder core has a core loss of 400 kW/m³ orless under the conditions of a frequency of 100 kHz and a magnetic fluxdensity of 0.1 T. This core loss is significantly smaller than that ofknown magnetic powder cores.

Preferably, the insulating material comprises a silicone rubber. Thesilicone rubber is effective for relieving the internal stress of themagnetic powder core.

Preferably, the glassy alloy is represented by the following formula:(Fe_(1−a)T_(a))_(100−x−v−z−w)Al_(x)(P_(1−b)Si_(b))_(v)C_(z)B_(w)wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent.

The magnetic powder core of the present invention is formed of the aboveFe-based glassy alloy powder in which the Fe content is higher than theCo and/or Ni content. Since this Fe-based glassy alloy exhibits highersaturation magnetic flux density than that of a Co-based glassy alloy,the magnetic powder core exhibits further improved magneticcharacteristics.

According to a second aspect of the present invention, a method formaking a magnetic powder core comprises a powder preparation step ofpreparing a powder of a glassy alloy comprising Fe and at least oneelement selected from Al, P, C, Si, and B, having a texture primarilycomposed of an amorphous phase, and exhibiting a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature, a molding step of mixing the glassy alloy powder with aninsulating material and compacting the mixture to form a magnetic coreprecursor, and an annealing step of annealing the magnetic coreprecursor at a temperature in the range between (T_(g)−170) K and T_(g)K to relieve the internal stress of the magnetic core precursor.

Preferably, the magnetic core precursor is annealed at a temperaturebetween (T_(g)−140) K and (T_(g)−60) K in the annealing step. Theinternal stress formed in the glassy alloy or the magnetic coreprecursor during the powder preparation step or the molding step isrelieved without crystallization of the glassy alloy.

More preferably, the magnetic core precursor is annealed at atemperature between (T_(g)−140) K and (T_(g)−60) K. When the magneticcore precursor is annealed at a temperature in the above range, theresulting magnetic powder core exhibits a coercive force of 80 A/m orless in an applied magnetic field of ±2.4 kA/m.

More preferably, the magnetic core precursor is annealed at atemperature between (T_(g)−110) K and (T_(g)−60) K. When the magneticcore precursor is annealed at a temperature in the above range, theresulting magnetic powder core exhibits a coercive force of 40 A/m orless in an applied magnetic field of ±2.4 kA/m.

In this method, the glassy alloy is preferably represented by thefollowing formula:(Fe_(1−a)T_(a))_(100−x−v−z−w)Al_(x)(P_(1−b)Si_(b))_(v)C_(z)B_(w)wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent.

According to a third aspect of the present invention, a switching powersupply comprises a switching element for converting a DC voltage into arectangular waveform voltage, a transformer for transforming therectangular waveform voltage, and a rectification circuit and asmoothing circuit for converting the transformed rectangular waveformvoltage into a DC voltage, wherein the transformer comprises a magneticcore comprising a molded article of a mixture of a glassy alloy powderand an insulating material, the glassy alloy powder having a textureprimarily composed of an amorphous phase and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

Since the switching power supply of the present invention includes atransformer having a magnetic core composed of a glassy alloy powder andan insulating material, the internal stress of the magnetic core can berelieved by annealing at a temperature which is sufficiently lower thanthe crystallization temperature of the glassy alloy, and the heatdissipation from the entire switching power supply can be reduced due toreduced core loss.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation, and does not generate a leakage magneticfield which adversely affects other peripheral circuit.

According to a fourth aspect of the present invention, a switching powersupply comprises a switching element for converting a DC voltage into arectangular waveform voltage, a transformer for transforming therectangular waveform voltage, and a rectification circuit and asmoothing circuit for converting the transformed rectangular waveformvoltage into a DC voltage, wherein the smoothing circuit comprises acapacitor and a coil provided with a magnetic core, the magnetic corecomprising a molded article of a mixture of a glassy alloy powder and aninsulating material, the glassy alloy powder comprising Fe and at leastone element selected from Al, P, C, Si, and B, having a textureprimarily composed of an amorphous phase, and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

Since the switching power supply of the present invention includes atransformer having a magnetic core composed of a glassy alloy powder,the internal stress of the magnetic core can be relieved by annealing ata temperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the heat dissipation from theentire switching power supply can be reduced due to reduced core loss.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation, and does not generate a leakage magneticfield which adversely affects other peripheral circuit.

According to a fifth aspect of the present invention, a step-downconverter circuit comprises a switching element, a coil provided with amagnetic core generating a back electromotive force when the switchingelement breaks a DC current, a capacitor for smoothing a currentgenerated by the back electromotive force, and a rectifying elementconnected to the coil provided with the magnetic core in an antiparallelstate, the rectifying element, the coil provided with the magnetic core,and the capacitor constituting a circulating current path, wherein themagnetic core comprises a molded article of a mixture of a glassy alloypowder and an insulating material, the glassy alloy having a textureprimarily composed of an amorphous phase and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

According to a sixth aspect of the present invention, a boostingconverter circuit comprises a switching element, a coil provided with amagnetic core generating a back electromotive force when the switchingelement breaks a DC current, a rectifying element connected in series inthe forward direction to the coil provided with the magnetic core forrectifying a current generated by the back electromotive force, and acapacitor for smoothing the rectified current, wherein the magnetic corecomprises a molded article of a mixture of a glassy alloy powder and aninsulating material, the glassy alloy having a texture primarilycomposed of an amorphous phase and exhibiting a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature.

According to a seventh aspect of the present invention, apolarity-reversing converter circuit comprises a switching element, acoil provided with a magnetic core generating a back electromotive forcewhen the switching element breaks a DC current, a capacitor forsmoothing a current generated by the back electromotive force, and arectifying element connected in series in the backward direction to thecoil provided with the magnetic core for blocking the DC current,wherein the magnetic core comprises a molded article of a mixture of aglassy alloy powder and an insulating material, the glassy alloy havinga texture primarily composed of an amorphous phase and exhibiting atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

In the step-down converter circuit, the boosting converter circuit, andthe polarity-reversing converter circuit, a magnetic core composed of aglassy alloy powder is used. Thus, the internal stress of the magneticcore can be relieved by annealing at a temperature which is sufficientlylower than the crystallization temperature of the glassy alloy, and theheat dissipation from the entire switching power supply can be reduceddue to reduced core loss.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation, and does not generate a leakage magneticfield which adversely affects other peripheral circuit.

According to an eighth aspect of the present invention, an active filtercomprises the above-described boosting converter circuit, and a controlunit for controlling the switching interval of the switching element ofthe boosting converter circuit.

The active filter of the present invention uses a coil with a magneticcore composed of a glassy alloy powder in the converter circuit therein.Since this magnetic core exhibits low loss, the heat dissipation fromthe entire active filter can be reduced.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation, and does not generate a leakage magneticfield which adversely affects other peripheral circuits.

In the above aspects, the magnetic core exhibits low core loss and lowpermeability, reducing heat dissipation. Moreover, the magnetic coreexhibiting low permeability does not require a gap for preventingmagnetic saturation, and does not generate a leakage magnetic field,which adversely affects other peripheral circuit.

Moreover, the insulating material enhances the resistivity of the entiremagnetic core and further reduces core loss due to reduced eddy currentloss.

According to a ninth aspect of the present invention, a filter comprisesa capacitor and an inductor of a coil wound around a magnetic core,wherein the magnetic core comprises a molded article of a mixture of aglassy alloy powder and an insulating material, the glassy alloy havinga texture primarily composed of an amorphous phase and exhibiting atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

In this filter, the internal stress of the glassy alloy can be relievedby annealing at a temperature which is sufficiently lower than thecrystallization temperature of the glassy alloy, and the magnetic coreexhibits low core loss and a substantially constant amplitudepermeability over a wide intensity range of magnetic field. Thus, thefilter exhibits reduced heat dissipation and outputs less distortedwaveforms.

Moreover, the insulating material enhances the resistivity of the entiremagnetic core and further reduces core loss due to reduced eddy currentloss. Since high permeability is maintained in a high-frequency region,the filter exhibits further improved high-frequency characteristics.

Preferably, the rate of change in amplitude permeability of the magneticcore in a magnetic field of 2,000 A/m is within ±10% of an amplitudepermeability in a magnetic field of 200 A/m, and the permeability of themagnetic core at 100 kHz is in the range of 50 to 200.

The filter outputs less distorted waveforms. Thus, the filter ispreferably applicable to a smoothing circuit of a pulse width modulatingamplifier.

Preferably, the filter is a low-pass filter. That is, the capacitor andthe inductor are connected into an L shape.

Preferably, the glassy alloy is represented by the following formula:(Fe_(1−a2)T_(a2))_(100−x2−v2−z2−w2)Al_(x2)(P_(1−b2)Si_(b2))_(v2)C_(z2)B_(w2)wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0<b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

Since the magnetic core composed of the glassy alloy having the abovecomposition exhibits reduced core loss and a substantially constantamplitude permeability over a variable magnetic field, the filter usingthe magnetic core exhibits reduced loss and reduced heat dissipation,and outputs waveforms with less distortion.

According to a tenth aspect of the present invention, an amplifyingdevice comprises an amplifier for outputting a pulsed current and afilter connected to the output side of the amplifier for smoothing thepulsed current, wherein the filter comprises a capacitor and an inductorof a coil wound around a magnetic core, wherein the magnetic corecomprises a molded article of a mixture of a glassy alloy powder and aninsulating material, the glassy alloy having a texture primarilycomposed of an amorphous phase and exhibiting a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature.

In the amplifying device of the present invention, the magnetic corecomposed of the glassy alloy powder and the insulating material. Theinternal stress of the magnetic core can be relieved by annealing at atemperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the heat dissipation from theamplifying device can be reduced due to reduced core loss. Theamplifying device outputs waveforms with less distortion.

Moreover, the insulating material enhances the resistivity of the entiremagnetic core and further reduces core loss due to reduced eddy currentloss. Since high permeability is maintained in a high-frequency region,the filter exhibits reduced loss and outputs waveforms with lessdistortion.

Preferably, the rate of change in amplitude permeability of the magneticcore in a magnetic field of 2,000 A/m is within ±10% of an amplitudepermeability in a magnetic field of 200 A/m, and the permeability of themagnetic core at 100 kHz is in the range of 50 to 200.

Within the above rate of change, the output waveform from the amplifyingdevice is less distorted. Moreover, the number of turns of the coil canbe reduced, thus resulting in a reduction in size of the amplifyingdevice.

Preferably, the filter is a low-pass filter.

Preferably, the amplifier is a pulse-width-modulation amplifier.

Preferably, the glassy alloy is represented by the following formula:(Fe_(1−a2)T_(a2))_(100−x2−v2−z2−w2)Al_(x2)(P_(1−b2)Si_(b2))_(v2)C_(z2)B_(w2)wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0<b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

Since the magnetic core composed of the glassy alloy having the abovecomposition exhibits reduced core loss and a substantially constantamplitude permeability over a variable magnetic field, the amplifyingdevice using the magnetic core exhibits reduced loss and outputswaveforms with less distortion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an embodiment of a magnetic powder corein accordance with the present invention;

FIG. 2 is an isometric partially broken-away view of a mold used in theproduction of a magnetic powder core in accordance with the presentinvention;

FIG. 3 is a schematic cross-sectional view of a discharge plasmasintering apparatus used in the production of a magnetic powder core inaccordance with the present invention;

FIG. 4 is a graph illustrating X-ray diffraction patterns of a tape anda powder of a glassy alloy having a composition ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃;

FIG. 5 is a DSC thermogram of a tape and a powder of a glassy alloyhaving a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃;

FIG. 6 is a graph illustrating the dependence of the magnetic fluxdensity on the annealing temperature of a magnetic powder corecontaining a glassy alloy having a composition ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ and an insulating layer in accordancewith the present invention;

FIG. 7 is a graph illustrating the dependence of the coercive force onthe annealing temperature of a magnetic powder core containing a glassyalloy having a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ and aninsulating layer in accordance with the present invention;

FIG. 8 is a graph illustrating the dependence of the magnetic fluxdensity on the annealing temperature of a magnetic powder core forcomparison containing powdered iron and an insulating layer;

FIG. 9 is a graph illustrating the dependence of the coercive force onthe annealing temperature of a magnetic powder core for comparisoncontaining powdered iron and an insulating layer;

FIG. 10 is a graph illustrating the dependence of the permeability (μ′)on the frequency (f) of a magnetic powder core containing a glassy alloyhaving a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ and aninsulating layer in accordance with the present invention;

FIG. 11 is a graph illustrating the dependence of the core loss (W) onthe frequency (f) of a magnetic powder core containing a glassy alloyhaving a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ and aninsulating layer in accordance with the present invention;

FIG. 12 is a graph illustrating the dependence of the permeability (μ′)on the frequency (f) of a magnetic powder core containing powdered ironand an insulating layer;

FIG. 13 is a graph illustrating the dependence of the core loss (W) onthe frequency (f) of a magnetic powder core containing powdered iron andan insulating layer;

FIG. 14 is a ternary diagram illustrating the dependence of the glasstransition temperature T_(g) on the compositionFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w) of a glassy alloy tape;

FIG. 15 is a ternary diagram illustrating the dependence of thecrystallization temperature T_(x) on the compositionFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w) of a glassy alloy tape;

FIG. 16 is a ternary diagram illustrating the dependence of thetemperature difference ΔT_(x) on the compositionFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w) in a supercooled liquid of aglassy alloy tape;

FIGS. 17A and 17B are graphs illustrating the dependence of thepermeability μ′ and the rate of change therein Δμ′, respectively, on theDC magnetic field H of a magnetic powder core;

FIGS. 18A and 18B are graphs illustrating the dependence of theinductance L and the rate of change therein ΔL, respectively, on the DCbias magnetic field H_(dc) of a magnetic powder core;

FIGS. 19A, 19B, and 19C are graphs illustrating the dependence of thepermeability μ′, the core loss W_(0.5/200k) and the core lossW_(1/100k), respectively, on the DC magnetic field H of a magneticpowder core;

FIG. 20 is a circuit diagram of a switching power supply in accordancewith an embodiment of the present invention;

FIG. 21 is an isometric view of a magnetic powder core of a transformerused in the switching power supply shown in FIG. 20;

FIG. 22 is a circuit diagram of a switching power supply in accordancewith an embodiment of the present invention.

FIG. 23 is a circuit diagram of a step-down converter circuit inaccordance with an embodiment of the present invention;

FIG. 24 is a circuit diagram of a boosting converter circuit inaccordance with an embodiment of the present invention;

FIG. 25 is a circuit diagram of a polarity-reversing converter circuitin accordance with an embodiment of the present invention;

FIG. 26 is a circuit diagram of an active filter in accordance with anembodiment of the present invention;

FIG. 27 is an isometric view of an inductor used in a filter inaccordance with an embodiment of the present invention;

FIG. 28 is a circuit diagram of an amplifying device in accordance withan embodiment of the present invention;

FIG. 29 is a graph illustrating a waveform of the input current to theamplifying device shown in FIG. 27;

FIG. 30 is a graph illustrating waveforms of input currents to a filterprovided in the amplifying device shown in FIG. 27;

FIG. 31 is a graph illustrating a waveform of an output current from theamplifying device shown in FIG. 27;

FIG. 32 is an isometric view of a mold used in the production ofinjection-molding articles;

FIGS. 33A and 33B are schematic views illustrating a method for makingan injection-molding article of an amorphous soft-magnetic alloy of thepresent invention using the mold shown in FIG. 32;

FIG. 34 is an isometric view illustrating an injection-molding articleand an injection-molding precursor of an amorphous soft-magnetic alloyof the present invention using the mold shown in FIG. 32;

FIG. 35 is a graph illustrating the dependence of the core loss (W) onthe frequency of a magnetic powder core of the present invention and amagnetic powder core for comparison;

FIG. 36 is a graph illustrating the dependence of the rate of change Δμ′in the amplitude permeability on the magnetic field of a magnetic powdercore of the present invention and a magnetic powder core for comparison;

FIG. 37 is a graph illustrating X-ray diffraction patterns of amorphoussoft-magnetic alloy tapes in accordance with EXAMPLES 6-1 to 6-14;

FIG. 38 is a graph illustrating DSC thermograms of amorphoussoft-magnetic alloy tapes of EXAMPLES 6-4 and 6-14 and COMPARATIVEEXAMPLE 6;

FIG. 39 is a ternary diagram illustrating the dependence of the glasstransition temperature T_(g) on the P, C, and B contents in amorphoussoft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 40 is a ternary diagram illustrating the dependence of thecrystallization temperature T_(x) on the P, C, and B contents inamorphous soft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 41 is a ternary diagram illustrating the dependence of thetemperature difference ΔT_(x) on the P, C, and B contents in supercooledliquids of amorphous soft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 42 is a ternary diagram illustrating the dependence of the meltingpoint T_(m) on the P, C, and B contents in amorphous soft-magnetic alloytapes represented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 43 is a ternary diagram illustrating the dependence of the ratioT_(g)/T_(m) on the P, C, and B contents in amorphous soft-magnetic alloytapes represented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 44 is a ternary diagram illustrating the dependence of the Curietemperature T_(c) on the P, C, and B contents in amorphous soft-magneticalloy tapes represented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 45 is a ternary diagram illustrating the dependence of thesaturation magnetization δs on the P, C, and B contents in amorphoussoft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 46 is a ternary diagram illustrating the dependence of thepermeability μe on the P, C, and B contents in amorphous soft-magneticalloy tapes represented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 47 is a ternary diagram illustrating the dependence of the coerciveforce Hc on the P, C, and B contents in amorphous soft-magnetic alloytapes represented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

FIG. 48 is a graph illustrating X-ray diffraction patterns of amorphoussoft-magnetic alloy tapes in accordance with EXAMPLES 7-15 to 7-18;

FIG. 49 is a ternary diagram illustrating the dependence of the glasstransition temperature T_(g) on the Fe and Al contents in amorphoussoft-magnetic alloy tapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 50 is a ternary diagram illustrating the dependence of thecrystallization temperature T_(x) on the Fe and Al contents in amorphoussoft-magnetic alloy tapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 51 is a ternary diagram illustrating the dependence of thetemperature difference ΔT_(x) on the Fe and Al contents in supercooledliquids of amorphous soft-magnetic alloy tapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 52 is a ternary diagram illustrating the dependence of the meltingpoint T_(m) on the Fe and Al contents in amorphous soft-magnetic alloytapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 53 is a ternary diagram illustrating the dependence of the ratioT_(g)/T_(m) on the Fe and Al contents in amorphous soft-magnetic alloytapes represented byFe_(100−x−y)A_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 54 is a ternary diagram illustrating the dependence of the Curietemperature T_(c) on the Fe and Al contents in amorphous soft-magneticalloy tapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 55 is a ternary diagram illustrating the dependence of thesaturation magnetization δs on the Fe and Al contents in amorphoussoft-magnetic alloy tapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 56 is a ternary diagram illustrating the dependence of thepermeability μe on the Fe and Al contents in amorphous soft-magneticalloy tapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 57 is a ternary diagram illustrating the dependence of the coerciveforce Hc on the Fe and Al contents in amorphous soft-magnetic alloytapes represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y);

FIG. 58 is a graph illustrating an X-ray diffraction pattern of aninjection-molding article in accordance with EXAMPLE 8-19;

FIG. 59 is a DSC thermogram of the injection-molding article inaccordance with EXAMPLE 8-19;

FIG. 60 is a graph illustrating a B-H curve of an injection-moldingarticle before annealing in accordance with EXAMPLE 8-19;

FIG. 61 is a graph illustrating a B-H curve of the injection-moldingarticle after annealing in accordance with EXAMPLE 8-19;

FIG. 62 is a graph illustrating a B-H curve of an injection-moldingarticle before annealing in accordance with COMPARATIVE EXAMPLE 2; and

FIG. 63 is a graph illustrating a B-H curve of the injection-moldingarticle after annealing in accordance with COMPARATIVE EXAMPLE 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a magnetic powder core and a method for makingthe same in accordance with the present invention will now describedwith reference to the drawings.

The magnetic powder core comprises a molded article of a mixture of aglassy alloy powder and an insulating material, the glassy alloycomprises Fe and at least one element Q selected from Al, P, C, Si, andB, has a texture primarily composed of an amorphous phase, and has atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature. Preferably, the glassy alloy has aresistivity of at least 1.5 μΩ.m.

FIG. 1 shows a toroidal magnetic powder core 1. The magnetic powder core1, however, may have any other shape, e.g., an ellipsoidal ring, an ovalring, an E shape, a U shape, or an I shape.

In the texture constituting the magnetic powder core, the glassy alloypowder is dispersed in the insulating material. Thus, the glassy alloypowder does not form a homogeneous texture which can be formed by themelt of the glassy alloy. Preferably, individual particles are insulatedfrom each other in the matrix of the insulating material. Thus, themagnetic powder core has large resistivity, reduced eddy current loss,and a moderated reduction in permeability in a high-frequency region.

When the temperature difference ΔT_(x) in the supercooled liquid of theglassy alloy is less than 20 K, it is difficult to adequately relievethe internal stress without crystallization at an annealing treatmentafter the compaction molding of the mixture of the glassy alloy powderand the insulating material. When the temperature difference ΔT_(x) isat least 20 K, the annealing can be performed at a lower temperaturewhich does not cause excess decomposition of the insulating layer andincreased loss.

In the magnetic powder core of the present invention, the magneticpowder has a coercive force of preferably 80 A/m or less and morepreferably 40 A/m or less in an applied magnetic field of ±2.4 kA/m.

The insulating material enhances resistivity of the magnetic powder coreand maintains the shape of the magnetic powder core by binding theglassy alloy powder. Insulating materials which do not cause large lossin magnetic properties are preferred. Examples of such insulatingmaterials include liquid or powdered organic compounds, e.g., epoxyresins, silicone resins, phenolic resins, urea resins, melamine resins,and polyvinyl alcohol (PVA); liquid glass, i.e., Na₂O—SiO₂; oxide glasspowders, e.g., Na₂O—B₂O₃—SiO₂, PbO—B₂O₃—SiO₂, PbO—BaO—SiO₂,Na₂O—B₂O₃—ZnO, CaO—BaO—SiO₂, Al₂O₃—B₂O₃—SiO₂, and B₂O₃—SiO₂; and glassysubstances formed by sol-gel processes and primarily composed of SiO₂,Al₂O₃, ZrO₂, and TiO₂.

The insulating material may be any elastomer, for example, a siliconerubber. The insulating material may be used together with a stearatesalt as a lubricant. Examples of stearate salts include zinc stearate,calcium stearate, barium stearate, magnesium stearate, and aluminumstearate.

The glassy alloy powder constituting the magnetic powder core of thepresent invention is prepared by pulverizing a tape of a glassy alloyhaving the above-mentioned composition, texture, and properties, byatomizing the melt of the glassy alloy onto a rotating cooling roller,by atomizing and cooling the melt of the glassy alloy with ahigh-pressure gas, or by atomizing the melt of the glassy alloy intowater. Since the glassy alloy powder has a texture primarily composed ofan amorphous phase, it exhibits superior soft magnetic characteristics,such as low coercive force.

In particular, the powder prepared by atomizing and cooling the melt ofthe glassy alloy with a high-pressure gas has higher sphericity comparedwith the powders prepared by the other processes, resulting in highprocessability and moldability. Accordingly, this powder is suitable forthe magnetic powder core of the present invention.

The glassy alloy has a large temperature difference ΔT_(x) of 40 K ormore and particularly 50 K or more, and has a large resistivity of atleast 1.5 μΩ.m in optimized compositions. These properties are notobtainable from conventional alloys. Moreover, the glassy alloy of thepresent invention exhibits the superior soft magnetic characteristics atroom temperature, unlike conventional alloys.

In the supercooled region, which correspond to the temperaturedifference ΔT_(x), the glassy alloy of the present invention maintains aliquid arrangement of atoms. The mobility of these atoms is so low thatcrystallization does not substantially occur, although atomic vibrationoccurs.

In the glassy alloy having a large temperature difference ΔT_(x), theatomic mobility is low during cooling the melt, and the supercooledliquid state is maintained over a broad temperature range. Since theglassy alloy of the present invention has a large temperature differenceΔT_(x) in a supercooled liquid, the alloy is readily supercooled to aglass transition temperature T_(g) below the crystallization temperatureT_(x) without being crystallized during a cooling step of the melt,readily forming an amorphous phase.

Thus, the amorphous phase can be formed at a relatively low coolingrate. For example, a glassy alloy powder primarily composed of anamorphous phase is obtainable by pulverizing a bulk glassy alloy, whichis prepared by a casting process, in addition to liquid quenchingprocesses having relatively high cooling rates, such as a single-rollerprocess.

The glassy alloy preferably used in the magnetic powder core of thepresent invention contains, for example, iron (Fe) as the majorcomponent, aluminum (Al), and at least one element Q selected from P, B,C, and Si. Preferably, the glassy alloy contains all of P, B, C, and Sirepresented by the element Q.

The glassy alloy may be represented by the following formula:(Fe_(1−a)T_(a))_(100−x−v−z−w)Al_(x)(P_(1−b)Si_(b))_(v)C_(z)B_(w)wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent.

Preferably, the subscripts a, b, x, v, z, and w satisfy therelationships, 0≦a≦0.15 by atomic ratio, 0.1 by atomic ratio≦b≦0.35 byatomic ratio, 0 atomic percent<x≦15 atomic percent, 8 atomicpercent<v≦18 atomic percent, 0.5 atomic percent≦z≦7.4 atomic percent,and 3 atomic percent≦w≦14 atomic percent. More preferably, thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0.1 by atomic ratio≦b≦0.28 by atomic ratio, 0 atomicpercent<x≦10 atomic percent, 11.3 atomic percent<v≦14 atomic percent,1.8 atomic percent≦z≦4.6 atomic percent, and 5.3 atomic percent≦w≦8.6atomic percent.

Fe—Al—Ga—C—P—Si—B glassy alloys are known. These glassy alloys containiron (Fe) and other elements which facilitate the formation of anamorphous phase, such as aluminum (Al), gallium (Ga), carbon (C),phosphorus (P), silicon (Si), and boron (B).

On the other hand, the glassy alloy of the present invention containsFe, Al, and at least one element Q selected from P, B, C, and Si. Thatis, the glassy alloy of the present invention does not contain Ga, butdoes contain an increased amount of Al. Thus, the present invention ischaracterized in that the glassy alloy of the present invention cancontain an amorphous phase regardless of the omission of Ga, which hasbeen considered to be an essential element for the formation of theamorphous layer, and that this glassy alloy has a large temperaturedifference ΔT_(x) in a supercooled liquid. These facts have beendiscovered by the present inventors.

Aluminum (Al) is an essential element for the amorphous soft-magneticalloy. At an Al content x of 20 atomic percent or less, this alloy has aperfect amorphous phase due to extremely enhanced amorphous formabilityof Al, and the amorphous soft-magnetic alloy has a temperaturedifference ΔT_(x) of 20 K or more in a supercooled liquid.

Since Al has a negative enthalpy of mixing with Fe and has an atomicradius which is larger than that of Fe, a combined use of Al with P, B,and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization and can yield a thermally stable amorphous structure.

The Al content x is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

Iron (Fe) is essential for the glassy alloy of the present invention asa magnetic element. In the present invention, Fe may be partiallyreplaced with at least one element T selected from Co and Ni. A higherFe content contributes to improved saturation magnetization of theresulting glassy alloy.

Carbon (C), phosphorus (P), silicon (Si), and boron (B) contribute tothe formation of an amorphous phase. A multicomponent system containingFe, Al, and these elements facilitates the formation of a more stableamorphous phase, compared with an Fe—Al binary system.

In particular, phosphorus (P) having high amorphous formabilityfacilitates the formation of a perfect amorphous phase over the entiretexture of the glassy alloy and ensures an adequate temperaturedifference ΔT_(x) in a supercooled liquid. Combined addition ofphosphorus and silicon causes a further increased temperature differenceΔT_(x) in a supercooled liquid.

When both phosphorus and silicon are added in combination, the totalcontent v of the phosphorus and silicon is preferably more than 0 to 22atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid.

The subscript b representing the relative Si and P contents by atomicratio is preferably in the range of 0<b≦0.8 when 0 atomic percent<v≦22atomic percent, 0.1≦b≦0.35 when 8 atomic percent≦v≦18 atomic percent, or0.1≦b≦0.28 when 11.3 atomic percent≦v≦14 atomic percent.

When the subscript b exceeds 0.8, an excess amount of Si may undesirablycause disappearance of the temperature difference ΔT_(x) in thesupercooled liquid.

Herein, the Si content in the glassy alloy is in the range of preferably17.6 atomic percent or less, more preferably 0.8 to 6.3 atomic percent,and most preferably 1.13 to 3.92 atomic percent.

The above-mentioned ranges for the subscripts b and v representing the Pand Si contents, respectively, contribute to an increased temperaturedifference ΔT_(x) in a supercooled liquid.

The subscript z representing the C content is in the range of preferablymore than 0 to 12 atomic percent, more preferably 0.5 to 7.4 atomicpercent, and most preferably 1.8 to 4.6 atomic percent.

The subscript w representing the B content is in the range of preferablymore than 0 to 16 atomic percent, more preferably 3 to 14 atomicpercent, and most preferably 5.3 to 8.6 atomic percent.

The glassy alloy may contain 4 atomic percent or less Ge, and 0 to 7atomic percent of at least one element selected from the groupconsisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

The glassy alloy of the present invention has a temperature differenceΔT_(x) of at least 20 K in the above-described composition, at least 35K in a particular composition, or at least 50 K in an optimizedcomposition.

The glassy alloy of the present invention may contain other incidentalimpurities.

An embodiment of a method for making the magnetic powder core inaccordance with the present invention will now be described withreference to the drawings.

The method for making the magnetic powder core includes a powderpreparation step of preparing a powder of a glassy alloy comprising Feand at least one element Q selected from Al, P, C, Si, and B, having atexture primarily composed of an amorphous phase, and exhibiting atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature, a molding step of mixing the glassy alloypowder with an insulating material and compacting the mixture to form amagnetic core precursor, and an annealing step of annealing the magneticcore precursor at a temperature in the range between (T_(g)−170) K andT_(g) K to relieve the internal stress of the magnetic core precursor.

In the powder preparation step, for example, a glassy alloy powder isprepared by pulverizing a glassy alloy tape and then classifying theparticles.

The glassy alloy tape is produced by a roller quenching process in whichthe melt of the glassy alloy is jetted onto a cold rotating roller sothat the melt is quenched. The glassy alloy tape may be pulverized usinga rotor mill, a ball mill, a jet mill, an atomizer, or a grinding mill.

The trituration is classified to select particles having a predeterminedaverage particle size. The average particle size of the powder ispreferably 30 μm or more and more preferably 45 μm to 300 μm. At anaverage particle size of less than 30 μm, particles may be contaminatedby a rotor mill or the like during pulverizing. At an average particlesize exceeding 300 μm, relatively large particles may cause theformation of voids in the magnetic powder core in a compaction moldingprocess of a mixture of the powder and an insulating material, resultingin undesirably large coercive force. The classification of thetrituration may be performed using a screen, a vibrating screen, anultrasonic screen, or an air-flow classifier.

In another embodiment of the powder preparation step, the mist of theglassy alloy melt having the above-mentioned composition is sprayed ontoa rotating cooling roller. In this process, glassy alloy powder iseasily obtained. The average particle size of the powder is determinedby controlling the rotation rate of the cooling roller, the temperatureof the melt, and spraying conditions.

The glassy alloy powder is also prepared by a gas atomizing process,which involves atomizing a glassy alloy melt with a high pressure gasinto a gaseous atmosphere for cooling, or by an aqueous atomizingprocess, which involves atomizing a glassy alloy melt into water forcooling.

In the gas atomizing process, a crucible with a jet nozzle is filledwith the glassy alloy melt maintained at a temperature which is at least140° C. higher than the melting point of the glassy alloy, and the meltis atomized with an inert gas, such as nitrogen or argon, of a pressureof at least 5.9 MPa. The gaseous atmosphere is preferably an inert gasatmosphere of, for example, argon or nitrogen, in order to preventoxidation of the alloy.

The atomized melt is instantaneously cooled and is converted intosubstantially spherical particles having a texture primarily composed ofan amorphous phase. In particular, the glassy alloy of the presentinvention containing Fe, Al, and at least one element Q selected from P,B, C, and Si exhibits high formability of an amorphous phase. Thus, anamorphous alloy can be produced by a gas atomizing process, which is notapplicable to conventional FeSiB-based alloys.

The average particle size of the glassy alloy powder prepared by a gasatomizing process is preferably in the range of 2 to 100 μm and morepreferably 2 to 60 μm. An average particle size of less than 2 μmdecreases the density of the compact, and the magnetic powder core has adecreased saturation magnetic flux density, a decreased permeability, anincreased coercive force, and an increased core loss. An averageparticle size exceeding 100 μm may cause the formation of voids in themagnetic powder core during compaction molding of a mixture of theglassy alloy powder and an insulating material, resulting in increasedcoercive force. Moreover, these particles have reduced cooling rates. Asa result, the amorphous phase has a decreased volume fraction in thetexture.

It is preferable that the average particle size of the resulting powderbe precisely controlled using a screen, a vibrating screen, anultrasonic screen, or an air-flow classifier, although the averageparticle size is controllable to some extent by the temperature of themelt and the gas pressure during the spraying operation.

In the subsequent molding step, the glassy alloy powder is mixed withthe above-mentioned insulating material, and the mixture is compacted toform a magnetic core precursor. The content of the insulating materialis preferably 0.3 weight percent to 5 weight percent and more preferably1 weight percent to 5 weight percent in the mixture. An insulatingmaterial content of less than 0.3 weight percent precludes molding ofthe mixture into a predetermined shape. An insulating material contentexceeding 5 weight percent causes deterioration of the soft magneticcharacteristics of the magnetic powder core due to a decreased glassyalloy content in the magnetic powder core. Prior to the compactionmolding, the solvents and moisture contained in the mixture arepreferably removed by evaporation so as to form an insulating layer onthe surface of the glassy alloy powder.

Next, the mixture is compacted to form a magnetic core precursor, usinga mold 10 shown in FIG. 2. The mold 10 substantially consists of ahollow cylindrical die 11, an upper punch 12, and a lower punch 13. Theupper punch 12 and the lower punch 13 will be inserted into a hollowsection 11 a of the hollow cylindrical die 11. The upper punch 12 has acylindrical protrusion 12 a on the bottom face thereof. An assembly ofthe upper punch 12, the lower punch 13, and the hollow cylindrical die11 forms a toroidal mold in the interior of the mold 10. The toroidalmold is filled with the above-mentioned mixture.

The mixture is heated to a predetermined temperature in the mold 10while applying a unidirectional pressure to compact the mixture.

FIG. 3 is a schematic cross-sectional view of a discharge plasmasintering apparatus which is suitable for compaction molding. Thedischarge plasma sintering apparatus has the mold 10 filled with themixture, a lower punch electrode 14, an upper punch electrode 15, and athermocouple 17 for measuring the temperature of the mixture in the mold10. The lower punch electrode 14 supports the lower punch 13 andfunctions as an electrode for applying a pulsed current, whereas theupper punch electrode 15 compresses the upper punch 12 downwardly andfunctions as another electrode for the pulsed current.

The discharge plasma sintering apparatus is placed in a chamber 18 whichis connected to a vacuum pumping system and an atmospheric gas supplyingsystem (both are not shown in the drawing) so that the mixture loadedinto the mold 10 is placed in a desired atmosphere, such as an inert gasatmosphere.

The lower punch electrode 14 and the upper punch electrode 15 areconnected to an energizing system (not shown in the drawing) so as tosupply electrical power between the lower punch 13 and the upper punch12.

The mold 10 filled with the mixture is placed into the discharge plasmasintering apparatus, and the apparatus is evacuated while the mixture isheated by a pulsed current applied to the upper punch 12 and the lowerpunch 13 under a unidirectional pressure P applied between the upperpunch 12 and the lower punch 13, to complete compaction molding.

Since the applied pulsed current can rapidly heat the mixture to apredetermined temperature in the discharge plasma sintering apparatus,the glassy alloy can be compacted within a short molding time withoutdeterioration of the amorphous phase.

The temperature during the compaction molding depends on the type of theinsulating material and the composition of the glassy alloy. In acombination of a liquid-glass insulating material and a glassy alloytape having a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃, thetemperature must be 373 K (100° C.) or more so that the glassy alloyparticles are bonded to each other in the matrix of the insulatingmaterial, and must be 673 K (400° C.) or less so that the meltedinsulating material does not ooze from the mold 10. If the insulatingmaterial oozes from the mold 10, the magnetic powder core has decreasedresistivity due to a decreased insulating material content, resulting indecreased permeability in a high-frequency region.

When the mixture is compacted at a temperature between 373 K (100° C.)and 673 K (400° C.), the insulating material is moderately softened sothat the glassy alloy particles are bonded to each other and the mixtureis maintained to a desired shape.

In compaction molding under a significantly low unidirectional pressureP, the density of the magnetic powder core is not increased, that is,the magnetic powder core is not dense. Under a high pressure P, theinsulating material oozes out, and the insulating material content inthe magnetic powder core decreases, resulting in decrease in resistivityand permeability in a high-frequency region. A preferred unidirectionalpressure P is determined by the type of the insulating material and thecomposition of the glassy alloy. In a combination of a liquid-glassinsulating material and a glassy alloy tape having a composition ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃, the unidirectional pressure P is inthe range of preferably 600 MPa to 1,500 MPa and more preferably 600 MPato 900 MPa. A toroidal magnetic core precursor is prepared in such amanner.

When a silicone rubber is used as the insulating material, a mixture ofthe glassy alloy powder and the silicone rubber can be compacted at roomtemperature in the above molding process to obtain a magnetic coreprecursor having a predetermined shape.

Since the silicone rubber has elasticity, the glassy alloy powderexhibits small hardening stress and small internal residual stress.Thus, the resulting glassy alloy exhibits improved soft magneticcharacteristics without the affection by magnetostriction. As a result,the magnetic powder core exhibits significantly improved coercive forceand core loss.

This magnetic powder core exhibits a core loss of 400 kW/m³ or less at afrequency of 100 kHz and a magnetic flux density of 0.1 T. This value issignificantly smaller than that of a conventional magnetic powder core.

When a significantly low pressure is applied to the mixture during thecompaction molding using the silicone rubber, the resulting magneticpowder core is not dense. When a significantly high pressure is applied,the silicone rubber oozes out, resulting in a decreased silicone rubbercontent in the magnetic powder core, and the resistivity of the magneticpowder core is decreased, resulting in decreased permeability at ahigh-frequency region. The preferred pressure depends on the compositionof the glassy alloy. When a glassy alloy having a composition ofFe₇₇Al₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87) is used, the pressure is in therange of preferably 500 MPa to 2,500 MPa and more preferably 1,000 MPato 2,000 MPa.

Next, an annealing step is performed for annealing the magnetic coreprecursor to relieve the internal stress thereof. The internal stressoccurs in the magnetic core precursor and the glassy alloy powder duringthe powder preparation step and the molding step. The stress is relievedby annealing the magnetic core precursor within a predeterminedtemperature difference. The resulting magnetic powder core exhibits lowcoercive force.

The annealing temperature is in the range of desirably (T_(g)−170) K to(T_(g)) K, preferably (T_(g)−160) K to (T_(g)−50) K, more preferably(T_(g)−140) K to (T_(g)−60) K, and (T_(g)−110) K to (T_(g)−60) K.

When the magnetic core precursor is annealed at a temperature between(T_(g)−160) K and (T_(g)−50), the magnetic powder core has a coerciveforce of 100 A/m or less at an applied magnetic field of ±2.4 kA/m. Whenthe magnetic core precursor is annealed at a temperature between(T_(g)−140) K and (T_(g)−60), the magnetic powder core has a coerciveforce of 80 A/m or less at an applied magnetic field of ±2.4 kA/m. Inaddition, when the magnetic core precursor is annealed at a temperaturebetween (T_(g)−110) K and (T_(g)−60), the magnetic powder core has acoercive force of 40 A/m or less at an applied magnetic field of ±2.4kA/m.

At an annealing temperature of less than (T_(g)−170) K, the internalstress in the magnetic core precursor is not sufficiently relieved. Atan annealing temperature exceeding (T_(g)) K, the alloy exhibits highcoercive force due to crystallization.

For example, in the case of a glassy alloy having a composition ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃, the annealing temperature is in therange of desirably 573 K (300° C.) to 723 K (450° C.), preferably 603 K(330° C.) to 713 K (440° C.), more preferably 623 K (350° C.) to 703 K(430° C.), and most preferably 653 K (380° C.) to 703 K (430° C.).

When a silicone rubber is used as the insulating material, the annealingtemperature is preferably in the range of 653 K (380° C.) to 703 K (430°C.). At an annealing temperature of less than 653 K, the internal stressin the magnetic core precursor is insufficiently relieved. At anannealing temperature exceeding 703 K, the silicone rubber issignificantly decomposed, resulting in decreased mechanical strength ofthe magnetic powder core. The silicone rubber is preferably annealed invacuum or in an inert gas atmosphere, such as a nitrogen atmosphere oran argon atmosphere. The nitrogen gas atmosphere is more preferable.

A toroidal magnetic powder core is formed by such annealing.

The resulting magnetic powder core containing the glassy alloy powderexhibits superior soft magnetic characteristics at room temperature andthe soft magnetic characteristics are further improved by annealing.This magnetic powder core is applicable to magnetic cores of variousmagnetic elements which require superior soft magnetic characteristics.

In addition to the above-described compaction molding in the dischargeplasma sintering apparatus, the mixture of the glassy alloy powder andthe insulating material may be compacted by conventional powder molding,hot pressing, or extruding.

In this embodiment, the toroidal magnetic powder core is manufacturedusing a mold. In an alternative embodiment, a bulk compact is preparedand is cut into various shapes, e.g., toroidal shapes, rods, E shapes,and U shapes. Magnetic powder cores having desired shapes can also beprepared in such a manner.

The magnetic powder core is formed of a mixture of the above-mentionedglassy alloy powder and the above-mentioned insulating material. Theinsulating material contributes to increased resistivity of the entiremagnetic powder core and reduced core loss due to decreased eddy currentloss in the magnetic powder core without decreased permeability in ahigh-frequency region.

When a glassy alloy having a resistivity of at least 1.5 μΩ.m is used,the resulting magnetic powder core shows further reduced core loss dueto reduced eddy current loss in the glassy alloy particles in ahigh-frequency region.

Since the magnetic core precursor is annealed at a temperature between(T_(g)−170) K and (T_(g)) K in this embodiment, the internal stress inthe glassy alloy or the magnetic core precursor is relieved withoutcrystallization of the glassy alloy. Thus, the magnetic powder coreexhibits low coercive force.

A glassy alloy powder prepared by an atomizing process using gas iscomposed of spherical particles having a small average particle size. Amagnetic powder core using this glassy alloy powder exhibits low coreloss, a high rate of change in permeability to a change in an appliedmagnetic field (amplitude permeability), and a high rate of change ininductance to a change in an applied magnetic field (DC-superimposingcharacteristic).

The silicone rubber as the insulating material does not require heatingduring compaction molding and can significantly reduce the internalstress in the magnetic powder core. Thus, the magnetic powder coreexhibits significantly reduced coercive force and core loss.

FIG. 20 shows an exemplary switching power supply 20 in accordance withthe present invention. This switching power supply 20 includes aswitching element 22, a transformer 23, a rectification circuit 24, anda smoothing circuit 25.

The switching element 22 consists of, for example, a switchingtransistor and converts a DC voltage from a DC power source 26 into arectangular pulsed current in response to a drive signal input through abase terminal.

The transformer 23 includes a magnetic core composed of the glassy alloyof the present invention. One input terminal is connected to the DCpower source 26, whereas the other is connected to the switching element22. The transformer 23 transforms the rectangular pulsed voltage fromthe switching element 22.

The rectification circuit 24 consists of, for example, a diode and isconnected to one output terminal.

The smoothing circuit 25 consists of, for example, a capacitor and isconnected to the output terminals of the transformer 23 in parallel.

The rectification circuit 24 and the smoothing circuit 25 convert therectangular pulsed voltage, which is transformed in the transformer 23,into a DC voltage Vout1 which is output through output terminals.

The magnetic core constituting the transformer 23 is a molded article ofa mixture of a glassy alloy powder and an insulating material, and theglassy alloy powder has a texture primarily composed of an amorphousphase and has a temperature difference ΔT_(x), which is represented bythe equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooledliquid, wherein T_(x) indicates the crystallization temperature andT_(g) indicates the glass transition temperature.

Preferably, the glassy alloy has a resistivity of at least 1.5 μΩ.m.

This magnetic core has low core loss and a low permeability in the rangeof 100 to 300 at a frequency of 100 kHz.

An exemplary shape of the magnetic core 30 is toroidal as shown in FIG.21. The magnetic core may have any other shape, for example, anellipsoidal or oval ring. Alternatively, the magnetic core may havesubstantially an E shape, a U shape, or an I shape, in a plan view.

The magnetic core 30 is formed of a glassy alloy powder which has acomposition described below and is present in a texture of an insulatingmaterial. This texture is not homogeneous, since the powder of theglassy alloy is not dissolved into the matrix. It is preferable that theglassy alloy particles be insulated from each other by the insulatingmaterial.

The insulating material increases the resistivity of the magnetic core30, resulting in decreased core loss due to reduced eddy current loss.

At a temperature difference ΔT_(x) of less than 20 K in the supercooledliquid of the glassy alloy, the glassy alloy will be inevitablycrystallized during annealing for relieving the internal stress. At atemperature difference ΔT_(x) exceeding 20 K, the internal stress can beadequately relieved without loss due to decomposition of the insulatingmaterial at a reduced temperature.

Since the glassy alloy having a specific composition has a temperaturedifference ΔT_(x) of 60 K or more, the internal stress in the magneticcore 30 can be adequately relieved during annealing. Thus, the magneticcore 30 exhibits improved soft magnetic characteristics without loss dueto deterioration of the insulating material during annealing at areduced temperature. Moreover, the magnetic core 30 exhibits low coreloss due to relaxation of the internal stress.

Since the magnetic core 30 has a permeability in the above-describedrange, the magnetic core 30 does not require a gap for preventingsaturation of the magnetic flux. Thus, no leakage magnetic field isgenerated.

It is preferable to use an insulating material which enhances theresistivity of the magnetic core 30, which binds the glassy alloyparticles so as to maintain the shape of the magnetic core 30, and whichdo not cause large loss of magnetic characteristics. Examples of suchinsulating materials include liquid or powdered organic compounds, e.g.,epoxy resins, silicone resins, phenolic resins, urea resins, melamineresins, and polyvinyl alcohol (PVA); liquid glass, i.e., Na₂O—SiO₂;oxide glass powders, e.g., Na₂O—B₂O₃—SiO₂, PbO—B₂O₃—SiO₂, PbO—BaO—SiO₂,Na₂O—B₂O₃—ZnO, CaO—BaO—SiO₂, Al₂O₃—B₂O₃—SiO₂, and B₂O₃—SiO₂; and glassysubstances formed by sol-gel processes and primarily composed of SiO₂,Al₂O₃, ZrO₂, and TiO₂.

The insulating material may be used together with a stearate salt as alubricant. Examples of stearate salts include zinc stearate, calciumstearate, barium stearate, magnesium stearate, and aluminum stearate.

The glassy alloy powder contains a primary phase having a resistivity ofat least 1.5 μ.Ω and a temperature difference ΔT_(x) of at least 20 K ina supercooled liquid. The glassy alloy powder is prepared by atomizingthe melt of the glassy alloy onto a cooling roller, by atomizing themelt of the glassy alloy together with a pressurized gas into theatmosphere, or by atomizing the melt of the glassy alloy into water. Theresulting glassy alloy powder exhibits low core loss and superior softmagnetic characteristics.

In the supercooled region, which correspond to the temperaturedifference ΔT_(x), the glassy alloy of the present invention maintains aliquid arrangement of atoms. The mobility of these atoms is so low thatcrystallization does not substantially occur, although atomic vibrationoccurs.

In the glassy alloy having a large temperature difference ΔT_(x), theatomic mobility is low during cooling the melt, and the supercooledliquid state is maintained over the large temperature difference.

Thus, the glassy alloy can have an adequate amorphous phase by arelatively low cooling rate. The glassy alloy primarily composed of theamorphous phase can be prepared, for example, by a liquid quenchingprocess having a relatively low cooling rate, such as a single rollerprocess, or by pulverizing a bulk glassy alloy prepared by a castingmethod.

The switching power supply 20 has the transformer 23 including themagnetic core 30 composed of the glassy alloy powder. The internalstress of the magnetic core 30 can be relieved by annealing at atemperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the heat dissipation from theentire switching power supply 20 can be reduced.

The magnetic core 30 exhibiting low permeability does not require a gapfor preventing magnetic saturation and does not generate a leakagemagnetic field which adversely affects the other peripheral circuits.

FIG. 22 shows a switching power supply as an embodiment of the presentinvention. The switching power supply 31 includes a switching element32, a transformer 33, a rectification circuit 34, and a smoothingcircuit 35.

The switching element 32 consists of, for example, a switchingtransistor and converts a DC voltage from a DC power source 36 into arectangular pulsed current in response to a drive signal input through abase terminal.

One input terminal is connected to the DC power source 36, whereas theother terminal is connected to the switching element 32. The transformer33 transforms the rectangular pulsed voltage from the switching element32.

The rectification circuit 34 consists of, for example, a pair of diodes34 a and is connected to the output side of the transformer 33. Thediode 34 a is connected in the backward direction with respect to theother diode 34 b in the circuit.

The smoothing circuit 35 consists of, for example, a capacitor 35 a anda coil 35 b with a magnetic core and is connected to the rectificationcircuit 34.

The rectification circuit 34 and the smoothing circuit 35 convert therectangular pulsed voltage, which is transformed in the transformer 33,into a DC voltage Vout2 which is output through output terminals.

As in the above embodiment, the magnetic core of the coil 35 is a moldedarticle of a mixture of a glassy alloy powder and an insulatingmaterial, and the glassy alloy powder has a texture primarily composedof an amorphous phase and has a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.

This magnetic core has low core loss and a low permeability in the rangeof 100 to 300 at a frequency of 100 kHz, as in the above-describedmagnetic core 30.

The switching power supply 31 includes the coil 35 b with the magneticcore composed of the glassy alloy powder. The internal stress of themagnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire switching power supply11 can be reduced.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation and does not generate a leakage magneticfield which adversely affects the other peripheral circuits.

FIG. 23 shows a step-down converter circuit as an embodiment of thepresent invention. The step-down converter circuit 41 includes aswitching element 42, a coil 43 with a magnetic core, a rectificationelement 44, and a capacitor 45.

The switching element 42 consists of, for example, a switchingtransistor, and intermittently interrupts the DC voltage Vin3, which isinput from the input terminal side, in response to a drive signal inputthrough a base terminal, and converts the voltage into a intermittent,rectangular pulsed current.

The coil 43 with the magnetic core is connected in series to theswitching element 42. As in the above magnetic core 30, the magneticcore of the coil 43 is a molded article of a mixture of a glassy alloypowder and an insulating material, and the glassy alloy powder has atexture primarily composed of an amorphous phase and has a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

Thus, this magnetic core also has low core loss and a low permeabilityin the range of 100 to 300 at a frequency of 100 kHz, as in theabove-described magnetic core 30.

The rectification element 44 consists of, for example, a diode and isconnected in the backward direction with respect to the switchingelement 42 and in parallel to the coil 43 with the magnetic core. Thecapacitor 45 is connected in parallel to an external load.

The coil 43 with the magnetic core, the rectification element 44, andthe capacitor 45 form a circulating current path. Thus, therectification element 44 functions as a circulating current diode.

When the switching element 42 is closed, a DC voltage (Vin3−Vout3) isgenerated in the coil 43. When the switching element 42 is opened, thecoil 43 generates a counterelectromotive force which causes acirculating current flow in the capacitor 45 and the rectificationelement 44.

When the open-close operations of the switching element 42 are repeated,the pulsed voltage are smoothed by the coil 43 with the magnetic coreand the capacitor 45 so that a DC voltage Vout3 (Vin3>Vout3) is outputthrough the output terminals.

In the step-down converter circuit 41, the magnetic core of the coil 43is composed of a glassy alloy powder. The internal stress of themagnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire step-down convertercircuit 41 can be reduced.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation and does not generate a leakage magneticfield which adversely affects the other peripheral circuits.

FIG. 24 shows a boosting converter circuit as an embodiment of thepresent invention. The boosting converter circuit 51 includes aswitching element 52, a coil 53 with a magnetic core, a rectificationelement 54, and a capacitor 55.

The switching element 52 consists of, for example, a switchingtransistor, and intermittently interrupts the DC voltage Vin4, which isinput from the input terminal side, in response to a drive signal inputthrough a base terminal, and converts the voltage into a intermittent,rectangular pulsed current.

The coil 53 with the magnetic core is connected in series to theswitching element 52. As in the above magnetic core, the magnetic coreof the coil 53 is a molded article of a mixture of a glassy alloy powderand an insulating material, and the glassy alloy powder has a textureprimarily composed of an amorphous phase and has a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

Thus, this magnetic core also has low core loss and a low permeabilityin the range of 100 to 300 at a frequency of 100 kHz, as in theabove-described magnetic core.

The rectification element 54 consists of, for example, a diode and isconnected in series to the coil 53 with the magnetic core and inparallel to the switching element 52. The capacitor 45 is connected inparallel to an external load.

When the switching element 52 is closed, a DC voltage Vin4 is generatedin the coil 53. In this mode, both input terminals are short-circuitedand no currents flow in the output side.

When the switching element 52 is opened, the coil 53 generates acounterelectromotive force and a current flows in the rectificationelement 54.

When the open-close operations of the switching element 42 are repeated,a current due to the counterelectromotive force intermittently flows inthe rectification element 54, and the intermittent current is smoothedby the capacitor 55 so that a DC voltage Vout4 (Vin4>Vout4) is outputthrough the output terminals.

In the step-down converter circuit 51, the magnetic core of the coil 53is composed of a glassy alloy powder. The internal stress of themagnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire boosting convertercircuit 51 can be reduced.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation and does not generate a leakage magneticfield which adversely affects the other peripheral circuits.

FIG. 25 shows a polarity-reversing converter circuit as an embodiment ofthe present invention. The polarity-reversing converter circuit 61includes a switching element 62, a coil 63 with a magnetic core, arectification element 64, and a capacitor 65.

The switching element 62 consists of, for example, a switchingtransistor, intermittently interrupts the DC voltage Vin5, which isinput from the input terminal side, in response to a drive signal inputthrough a base terminal, and converts the voltage into a intermittent,rectangular pulsed current.

The coil 63 with the magnetic core is connected in series to theswitching element 62. The magnetic core of the coil 63 is also a moldedarticle of a mixture of a glassy alloy powder and an insulatingmaterial, and the glassy alloy powder has a texture primarily composedof an amorphous phase and has a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.

Thus, this magnetic core also has low core loss and a low permeabilityin the range of 100 to 300 at a frequency of 100 kHz, as in theabove-described magnetic core.

The rectification element 64 consists of, for example, a diode and isconnected in the backward direction in series to the switching element62. The capacitor 65 is connected in parallel to an external load.

When the switching element 62 is closed, a current i1 generated by a DCvoltage Vin5 flows in the coil 63. Since the rectification element 44 isconnected backward to the switching element 42, no currents flow in theoutput side.

When the switching element 62 is opened, the coil 63 generates acounterelectromotive force and a current i2 flows in the capacitor 65.

When the open-close operations of the switching element 62 are repeated,a current i2 due to the counterelectromotive force intermittently flowsin the capacitor 65 so that a DC voltage −Vout5 is generated between theboth terminals of the capacitor 65.

The DC voltage Vin5 having a positive polarity is output as a DC voltageVout5 having a negative polarity through the output terminals.

In the step-down converter circuit 61, the magnetic core of the coil 63is composed of a glassy alloy powder. The internal stress of themagnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire polarity-reversingconverter circuit 61 can be reduced.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation and does not generate a leakage magneticfield which adversely affects the other peripheral circuits.

FIG. 26 shows an active filter as an embodiment of the presentinvention. The active filter 71 is called a boosting PWM-type activefilter, and includes a control unit 72, a start circuit 73, arectification circuit 74, a noise filter circuit 75, and the boostingconverter circuit 51 described in the former embodiment.

The control unit 72 is, for example, an active filter monolithic IChaving an oscillator, a controlling amplifier, a multiplier, and acurrent detector, and controls the switching interval of the switchingelement 52 in the boosting converter circuit 51.

The start circuit 73 detects a current flowing in the coil 53 with themagnetic core and controls the switching interval of the switchingelement 52 in the boosting converter circuit 51 to control the rushcurrent when a voltage is input.

The rectification circuit 74 converts the AC voltage from the input sideinto a pulsating flow, while the noise filter circuit 75 removes noisegenerated by the boosting converter circuit 51.

The boosting converter circuit 51 includes, as described above, theboosting converter circuit 51, the coil 53 with the magnetic core, therectification element 54, and the capacitor 55.

The pulsating flow from the rectification circuit 74 is applied to theswitching element 52 when the switching element 52 is closed. When theswitching element 52 is opened, a counterelectromotive force isgenerated in the coil 53 with the magnetic core so that a current flowsin the rectification element 54.

The control unit 72 controls the open-close operations of the switchingelement 52. When the open-close operations of the switching element 52are repeated, a current due to the counterelectromotive forceintermittently flows in the rectification circuit 34, and this currentis smoothed by the capacitor 55 so that a DC voltage is output throughthe output terminals. Since this circuit does not require a smoothingcircuit at the input side, the input current does not include harmonicdistortion.

The magnetic core of the coil 53 is also a molded article of a mixtureof a glassy alloy powder and an insulating material, and the glassyalloy powder has a texture primarily composed of an amorphous phase andhas a temperature difference ΔT_(x), which is represented by theequation ΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid,wherein T_(x) indicates the crystallization temperature and T_(g)indicates the glass transition temperature.

Thus, this magnetic core also has low core loss and a low permeabilityin the range of 100 to 300 at a frequency of 100 kHz, as in theabove-described magnetic core.

In the active filter 71, the magnetic core of the coil 53 is composed ofa glassy alloy powder. The internal stress of the magnetic core can berelieved by annealing at a temperature which is sufficiently lower thanthe crystallization temperature of the glassy alloy, and the heatdissipation from the entire active filter 71 can be reduced.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation and does not generate a leakage magneticfield which adversely affects the other peripheral circuits.

The composition of the glassy alloy in accordance with the presentinvention will now be described in detail.

The glassy alloy used in the magnetic core is primarily composed of Fe,and contains Al and the element Q. The element Q may not include Si.

The glassy alloy is represented by, for example, the following formula:(Fe_(1−a2)T_(a2))_(100−x2−v2−z2−w2)Al_(x2)(P_(1−b2)Si_(b2))_(v2)C_(z2)B_(w2)wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0<b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

When the glassy alloy has the above composition, the temperaturedifference ΔT_(x) in a supercooled liquid is at least 20 K.

Preferably, the subscripts a2, b2, x2, v2, z2, and w2 satisfy therelationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.35 by atomic ratio, 0atomic percent<x2≦15 atomic percent, 8 atomic percent≦v2≦18 atomicpercent, 0.5 atomic percent≦z2≦7.4 atomic percent, and 3 atomicpercent≦w2≦14 atomic percent.

When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in a supercooled liquid is 40 K or more.

More preferably, the subscripts a2, b2, x2, v2, z2, and w2 satisfy therelationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.28 by atomic ratio, 0atomic percent<x2≦10 atomic percent, 11.3 atomic percent≦v2≦14 atomicpercent, 1.8 atomic percent≦z2≦4.6 atomic percent, and 5.3 atomicpercent≦w2≦8.6 atomic percent.

When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in a supercooled liquid is 60 K or more.

The glassy alloy of the present invention contains Fe, Al, and at leastone element Q. That is, the glassy alloy of the present invention doesnot contain Ga, which is contained in a conventional GeAlGaPCB(Si)alloy, but does contain an increased amount of Al. Thus, this glassyalloy has a large temperature difference ΔT_(x) in a supercooled liquidand exhibits significantly enhanced formability of the amorphous phase.

Since the glassy alloy exhibits significantly enhanced amorphous phaseformability, the entire texture can be composed of a perfect amorphousphase. Thus, the permeability and the saturation magnetization aresignificantly improved, resulting in superior soft magneticcharacteristics.

Moreover, the internal stress of the glassy alloy can be relievedwithout precipitation of the crystalline phase during annealing underproper conditions due to the perfect amorphous phase, resulting infurther improved soft magnetic characteristics.

Aluminum (Al) is an essential element for this glassy alloy. At an Alcontent x of 20 atomic percent or less, this alloy has a perfectamorphous phase due to extremely enhanced amorphous formability of Al,and the amorphous alloy has a temperature difference ΔT_(x) of at least20 K in a supercooled liquid.

Since Al has a negative enthalpy of mixing with Fe and has an atomicradius which is larger than that of Fe, a combined use of Al with P, B,and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization, and can yield a thermally stable amorphous structure.

Moreover, Al raises the Curie temperature of the glassy alloy andimproves thermal stability of various magnetic characteristics.

The Al content x2 is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x2 exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

Iron (Fe) is essential for the glassy alloy of the present invention asa magnetic element. In the present invention, Fe may be partiallyreplaced with at least one element T selected from Co and Ni. A higherFe content contributes to improved saturation magnetization of theresulting glassy alloy.

Carbon (C), phosphorus (P), silicon (Si), and boron (B) as the element Qcontribute to the formation of an amorphous phase.

When both phosphorus and silicon are added in combination, the totalcontent v2 of the phosphorus and silicon is preferably more than 0 to 22atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v2 contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid.

The subscript b2 representing the relative Si and P contents by atomicratio is preferably in the range of 0<b2≦0.8 when 0 atomic percent<v2≦22atomic percent, 0.1≦b≦0.35 when 8 atomic percent≦v2≦18 atomic percent,or 0.1≦b2≦0.28 when 11.3 atomic percent≦v≦14 atomic percent.

When the subscript b2 exceeds 0.8, an excess amount of Si mayundesirably cause disappearance of the temperature difference ΔT_(x) inthe supercooled liquid.

Herein, the Si content in the glassy alloy is in the range of preferably17.6 atomic percent or less, more preferably 0.8 to 6.3 atomic percent,and most preferably 1.13 to 3.92 atomic percent.

The above-mentioned ranges of the subscripts b2 and v2 representing theP and Si contents, respectively, contribute to an increased temperaturedifference ΔT_(x) in a supercooled liquid.

The subscript z2 representing the C content is in the range ofpreferably more than 0 to 12 atomic percent, more preferably 0.5 to 7.4atomic percent, and most preferably 1.8 to 4.6 atomic percent.

The subscript w2 representing the B content is in the range ofpreferably more than 0 to 16 atomic percent, more preferably 3 to 14atomic percent, and most preferably 5.3 to 8.6 atomic percent.

The glassy alloy may contain 4 atomic percent or less Ge, and 0 to 7atomic percent of at least one element selected from the groupconsisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

The glassy alloy of the present invention has a temperature differenceΔT_(x) of at least 35 K in the above-described composition or at least50 K in an optimized composition.

The glassy alloy of the present invention may contain other incidentalimpurities.

This magnetic core can be produced by the above-described method.

The magnetic core composed of the above composition exhibiting low coreloss and permeability suppresses heat dissipation during operation, doesnot require a gap for preventing magnetic saturation, and does notgenerate a leakage magnetic field which adversely affects the otherperipheral circuits.

Since the glassy alloy used has a resistivity of at least 1.5 μΩ.m, theresulting magnetic powder core shows further reduced core loss due toreduced eddy current loss in the glassy alloy particles in ahigh-frequency region. As a result, the magnetic core exhibits furtherreduced core loss and heat dissipation.

Moreover, the insulating material contributes to an increase inresistivity of the entire magnetic core. Thus, the magnetic coreexhibits further reduced core loss due to decreased eddy current loss.

The above embodiments describe the formation of the magnetic core bydischarge plasma sintering compaction molding of a mixture of a glassyalloy powder and a insulating material. The magnetic core, however, maybe formed by any other process, for example, a conventional powdermolding process, a hot pressing process, or an extruding process.

A filter in accordance with the present invention comprises a capacitorand an inductor of a coil wound around a magnetic core, wherein themagnetic core comprises a molded article of a mixture of a glassy alloypowder and an insulating material, the glassy alloy having a textureprimarily composed of an amorphous phase and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

This filter is mounted at the output side of an amplifier to smooth anoutput current from the amplifier. An example of the amplifying devicehaving this filter includes an amplifier for outputting a pulsed currentand a filter connected to the output side of the amplifier for smoothingthe pulsed current.

FIG. 27 shows an inductor used in the filter in accordance with thepresent invention, and FIG. 28 is a circuit diagram of an amplifyingdevice provided with this filter.

As shown in FIG. 27, the inductor 81 includes a magnetic core 82 and acoil 83 wound therearound. As shown in FIG. 28, the amplifying device 84includes an amplifier 85 for outputting a pulsed current and a filter 86in accordance with the present invention which is connected to outputterminals 85 b of the amplifier 85 and smoothes the pulsed current fromthe amplifier 85. The filter 86 consists of a capacitor 87 and theinductor 81 shown in FIG. 27.

The filter 86 is a so-called low-pass filter in which the capacitor 87and the inductor 81 are connected to each other so as to form an Lshape. Preferably, the amplifier 85 is a pulse-width modulationamplifier.

The operation of the amplifying device 84 will now be described.

An AC current with a voltage V1 shown in FIG. 29 is input to inputterminals 85 a of the amplifier 85. The amplifier 85 convertshigh-voltage portions of the input AC voltage into broader pulse wavesand low-voltage portions into narrower pulse waves. Moreover, theamplifier 85 amplifies the voltage and outputs the pulsed current shownin FIG. 30 through the output terminals 85 b. The filter 86 smoothesthis pulsed current and outputs the smoothed current through outputterminals 86 a of the filter 86. The output current is an amplified ACcurrent of a voltage V2 (V2>V1) as shown in FIG. 31.

As described above, a pulsed current is input to the filter 86 inaccordance with the present invention. Since the width and the voltageof the pulsed current periodically vary, a high-frequency current isapplied to the inductor 81.

In order to achieve an amplifying device with low loss and reducedwaveform distortion, the loss of the inductor 81 must be reduced. Thus,the requirements for the magnetic core 82 constituting the inductor 81are low core loss and substantially constant amplitude permeability witha change in magnetic field.

The magnetic core 82 constituting the filter of the present invention isa molded article of a mixture of a glassy alloy powder havingresistivity of at least 1.5 μΩ.cm and an insulating material, and theglassy alloy powder has a texture primarily composed of an amorphousphase and has a temperature difference ΔT_(x), which is represented bythe equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooledliquid, wherein T_(x) indicates the crystallization temperature andT_(g) indicates the glass transition temperature.

The magnetic core 82 shown in FIG. 27 is toroidal. The shape of themagnetic core 82, however, is not limited to this. For example, themagnetic core 82 may be ellipsoidal, oval, E-shaped, U-shaped, orI-shaped in a plan view.

The magnetic core 82 is composed of a magnetic powder core in whichglassy alloy particles are bonded to each other with an insulatingmaterial and are dispersed in the texture. Thus, the glassy alloyparticles are not dissolved into the matrix as a uniform texture. Theindividual glassy alloy particles are preferably insulated from eachother in the insulating material. Accordingly, the magnetic core 82 haslarge resistivity due to the effects of the insulating material, lowcore loss due to reduced eddy current loss, less reduction inpermeability in a high-frequency region and substantially constantamplitude permeability with a change in magnetic field.

When the temperature difference ΔT_(x) in the supercooled liquid of theglassy alloy is less than 20 K, it is difficult to adequately relievethe internal stress without crystallization at an annealing treatmentafter the compaction molding of the mixture of the glassy alloy powderand the insulating material. When the temperature difference ΔT_(x) isat least 20 K, the annealing can be performed at a lower temperaturewhich does not cause excess decomposition of the insulating layer andincreased loss.

Since the glassy alloy having a specific composition has a temperaturedifference ΔT_(x) of 60 K or more, the internal stress in the magneticcore 82 can be adequately relieved during annealing. Thus, the magneticcore 82 exhibits improved soft magnetic characteristics without loss dueto deterioration of the insulating material during annealing at areduced temperature. Moreover, the magnetic core 82 exhibits low coreloss due to relaxation of the internal stress during the annealing andreduces heat dissipation.

The magnetic core 82 shows a small change in permeability with a changein operational frequency and high permeability in high-frequency ranges,contributing improved frequency characteristics of the filter 86.

Preferably, the rate of change in amplitude permeability of the magneticcore 82 in a magnetic field of 2,000 A/m is within ±10% of an amplitudepermeability in a magnetic field of 200 A/m, and the permeability of themagnetic core at 100 kHz is in the range of 50 to 200.

Within the above rate of change, the output waveform from the filter 86is less distorted. Moreover, the number of turns of the coil 83 can bereduced, thus resulting in a reduction in size of the inductor 81.Accordingly, the sizes of the filter 86 and the amplifying device 84 canbe reduced. For example, the filter 86 exhibits superior characteristicswhen the number of turns of the coil 83 is 30.

The insulating material enhances resistivity of the magnetic core 82 andmaintains the shape of the magnetic core 82 by binding the glassy alloyparticles. Insulating materials which do not cause large loss inmagnetic properties are preferred. Examples of such insulating materialsinclude liquid or powdered organic compounds, e.g., epoxy resins,silicone resins, phenolic resins, urea resins, melamine resins, andpolyvinyl alcohol (PVA); liquid glass, i.e., Na₂O—SiO₂; oxide glasspowders, e.g., Na₂O—B₂O₃—SiO₂, PbO—B₂O₃—SiO₂, PbO—BaO—SiO₂,Na₂O—B₂O₃—ZnO, CaO—BaO—SiO₂, Al₂O₃—B₂O₃—SiO₂, and B₂O₃—SiO₂; and glassysubstances formed by sol-gel processes and primarily composed of SiO₂,Al₂O₃, ZrO₂, and TiO₂.

The insulating material may be used together with a stearate salt as alubricant. Examples of stearate salts include zinc stearate, calciumstearate, barium stearate, magnesium stearate, and aluminum stearate.

The glassy alloy powder contains a primary phase having a resistivity ofat least 1.5 μ.Ω and a temperature difference ΔT_(x) of at least 20 K ina supercooled liquid. The glassy alloy powder is prepared by pulverizinga glassy alloy tape, by atomizing the melt of the glassy alloy onto acooling roller, by atomizing the melt of the glassy alloy together witha pressurized gas into the atmosphere, or by atomizing the melt of theglassy alloy into water. The resulting glassy alloy powder exhibits lowcore loss and superior soft magnetic characteristics.

The glassy alloy has a large temperature difference ΔT_(x) of 40 K ormore, particularly 50 K or more, and more particularly 60 k or more, andhas a large resistivity of at least 1.5 μΩ.m under optimizedcompositions. These properties are not obtainable from conventionalalloys. Moreover, the glassy alloy exhibits the superior soft magneticcharacteristics at room temperature, unlike conventional alloys.

In the supercooled region, which correspond to the temperaturedifference ΔT_(x), the glassy alloy of the present invention maintains aliquid arrangement of atoms. The mobility of these atoms is so low thatcrystallization does not substantially occur, although atomic vibrationoccurs.

In the glassy alloy having a large temperature difference ΔT_(x), theatomic mobility is low during cooling the melt, and the supercooledliquid state is maintained over a broad temperature range. Since theglassy alloy of the present invention has a large temperature differenceΔT_(x) in a supercooled liquid, the alloy is readily supercooled to atemperature below a glass transition temperature T_(g) without beingcrystallized during a cooling step of the melt, readily forming anamorphous phase.

Thus, the amorphous phase can be formed at a relatively low coolingrate. For example, a glassy alloy powder primarily composed of anamorphous phase is obtainable by pulverizing a bulk glassy alloy, whichis prepared by a casting process, in addition to liquid quenchingprocesses having relatively high cooling rates, such as a single-rollerprocess.

The glassy alloy used in the magnetic core 82 is primarily composed ofFe, and contains Al and the element Q. The element Q may not include Si.

The glassy alloy is represented by, for example, the following formula:(Fe_(1−a2)T_(a2))_(100−x2−v2−z2−w2)Al_(x2)(P_(1−b2)Si_(b2))_(v2)C_(z2)B_(w2)wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0<b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

When the glassy alloy has the above composition, the temperaturedifference ΔT_(x) in a supercooled liquid is at least 20 K.

Preferably, the subscripts a2, b2, x2, v2, z2, and w2 satisfy therelationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.35 by atomic ratio, 0atomic percent<x2≦15 atomic percent, 8 atomic percent≦v2≦18 atomicpercent, 0.5 atomic percent≦z2≦7.4 atomic percent, and 3 atomicpercent≦w2≦14 atomic percent.

When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in the supercooled liquid is 40 K or more.

More preferably, the subscripts a2, b2, x2, v2, z2, and w2 satisfy therelationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.28 by atomic ratio, 0atomic percent<x2≦10 atomic percent, 11.3 atomic percent≦v2≦14 atomicpercent, 1.8 atomic percent≦z2≦4.6 atomic percent, and 5.3 atomicpercent≦w2≦8.6 atomic percent.

When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in the supercooled liquid is 60 K or more.

The glassy alloy of the present invention contains Fe, Al, P, C, B, andSi. That is, the glassy alloy of the present invention does not containGa, which is contained in a conventional GeAlGaPCB(Si) alloy, but doescontain an increased amount of Al. Thus, this glassy alloy has a largetemperature difference ΔT_(x) in a supercooled liquid and exhibitssignificantly enhanced formability of the amorphous phase.

Since the glassy alloy exhibits significantly enhanced amorphous phaseformability, the entire texture can be composed of a perfect amorphousphase. Thus, the permeability and the saturation magnetization aresignificantly improved, resulting in superior soft magneticcharacteristics.

Aluminum (Al) is an essential element for this glassy alloy. At an Alcontent x of 20 atomic percent or less, this alloy has a perfectamorphous phase due to extremely enhanced amorphous formability of Al,and the amorphous alloy has a temperature difference ΔT_(x) of at least20 K in a supercooled liquid.

Since Al has a negative enthalpy of mixing with Fe and has an atomicradius which is larger than that of Fe, a combined use of Al with P, B,and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization and can yield a thermally stable amorphous structure.

Moreover, Al raises the Curie temperature of the glassy alloy andimproves thermal stability of various magnetic characteristics.

The Al content x2 is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x2 exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

Iron (Fe) is essential for the glassy alloy of the present invention asa magnetic element. In the present invention, Fe may be partiallyreplaced with at least one element T selected from Co and Ni. A higherFe content contributes to improved saturation magnetization of theresulting glassy alloy.

Carbon (C), phosphorus (P), silicon (Si), and boron (B) as the element Qcontribute to the formation of an amorphous phase.

When both phosphorus and silicon are added in combination, the totalcontent v2 of the phosphorus and silicon is preferably more than 0 to 22atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v2 contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid.

The subscript b2 representing the relative Si and P contents by atomicratio is preferably in the range of 0<b2≦0.8 when 0 atomic percent<v2≦22atomic percent, 0.1≦b≦0.35 when 8 atomic percent<v2≦18 atomic percent,or 0.1≦b2≦0.28 when 11.3 atomic percent≦v≦14 atomic percent.

When the subscript b2 exceeds 0.8, an excess amount of Si mayundesirably cause disappearance of the temperature difference ΔT_(x) inthe supercooled liquid.

Herein, the Si content in the glassy alloy is in the range of preferably17.6 atomic percent or less, more preferably 0.8 to 6.3 atomic percent,and most preferably 1.13 to 3.92 atomic percent.

The above-mentioned ranges of the subscripts b2 and v2 representing theP and Si contents, respectively, contribute to an increased temperaturedifference ΔT_(x) in a supercooled liquid.

The subscript z2 representing the C content is in the range ofpreferably more than 0 to 12 atomic percent, more preferably 0.5 to 7.4atomic percent, and most preferably 1.8 to 4.6 atomic percent.

The subscript w2 representing the B content is in the range ofpreferably more than 0 to 16 atomic percent, more preferably 3 to 14atomic percent, and most preferably 5.3 to 8.6 atomic percent.

The glassy alloy may contain 4 atomic percent or less Ge, and 0 to 7atomic percent of at least one element selected from the groupconsisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

The glassy alloy of the present invention has a temperature differenceΔT_(x) of at least 35 K in the above-described composition or at least50 K in an optimized composition.

The glassy alloy of the present invention may contain other incidentalimpurities.

This magnetic core can also be produced by the above-described method.

The resulting magnetic core 82 containing the glassy alloy exhibitssuperior soft magnetic characteristics at room temperature and the softmagnetic characteristics are further improved by annealing. Thismagnetic core 82 exhibits reduced core loss compared to that ofconventional materials and substantially constant permeability with achange in magnetic field, and is preferably used in the filter 86 whichrequires superior soft magnetic characteristics.

In addition to the above-described compaction molding in the dischargeplasma sintering apparatus, the magnetic core 82 may be formed by othercompaction molding processes, such as conventional powder molding, hotpressing, and extruding.

The filter 86 includes the magnetic core 82, which is formed of amixture of the above-mentioned glassy alloy powder and theabove-mentioned insulating material. The insulating material contributesto increased resistivity of the entire magnetic powder core and reducedcore loss due to decreased eddy current loss in the magnetic core 82.The resulting filter 86 exhibits low loss and less heat dissipation.Moreover, the magnetic core 82 composed of the glassy alloy powderexhibits a small reduction in permeability in a high-frequency region,thus resulting in improved frequency characteristics of the filter 86.

Since the magnetic core 82 contains the glassy alloy having aresistivity of at least 1.5 μΩ.m, the resulting magnetic core showsfurther reduced core loss due to reduced eddy current loss in the glassyalloy particles in a high-frequency region. The resulting filter 86exhibits low loss and less heat dissipation.

Since the rate of change in amplitude permeability of the magnetic core82 in a magnetic field of 2,000 A/m is within ±10% of an amplitudepermeability in a magnetic field of 200 A/m, the pulsed AC current canbe smoothed without waveform distortion, the filter 86 outputtingwaveforms with less distortion.

Moreover, the magnetic core 82 has a permeability of the magnetic corein the range of 50 to 200 at 100 kHz. Thus, the size of the inductor 81can be reduced by decreasing the number of turns of the coil 83, thusreduction in size of the filter 86 or the amplifying device 84.

The amplifying device 84 including the filter 86 with low loss andreduced waveform distortion exhibits reduced heat dissipation andoutputs a current with reduced distortion.

The composition of the glassy alloy in accordance with the presentinvention will now be described in more detail.

The amorphous soft-magnetic alloy of the present invention comprises Fe,Al, P, C, Si, and B and has a texture primarily composed of an amorphousphase. In addition, this amorphous alloy has a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature.

Since the amorphous soft-magnetic alloy of the present inventioncontains Fe as a magnetic component and Al, P, C, Si, and B havingamorphous formability, the amorphous alloy exhibits superior softmagnetic characteristics.

In particular, an amorphous soft-magnetic alloy exhibiting a temperaturedifference ΔT_(x) of at least 20 K in a supercooled liquid is called aglassy alloy. The glassy alloy can has a temperature difference ΔT_(x)of at least 40 K and particularly at least 60 K in an optimizedcomposition, which is not anticipated from conventional knowledge. Theglassy alloy also exhibits superior soft magnetic characteristics atroom temperature.

The amorphous soft-magnetic alloy primarily composed of an amorphousphase has small coercive force and thus exhibits superior soft magneticcharacteristics.

Since the amorphous soft-magnetic alloy of the present invention has alarge temperature difference ΔT_(x) in a supercooled liquid, the alloyis readily supercooled to a temperature below a glass transitiontemperature T_(g) without being crystallized during a cooling step ofthe melt, readily forming an amorphous phase. Thus, the amorphous phasecan be formed at a relatively low cooling rate. For example, a glassyalloy powder primarily composed of an amorphous phase is obtainable bypulverizing a bulk glassy alloy, which is prepared by a casting orinjection process, in addition to liquid quenching processes havingrelatively high cooling rates, such as a single-roller process.

Moreover, the amorphous soft-magnetic alloy of the present inventionexhibits a high Curie temperature and superior thermal stability.

The glassy alloy may be represented by the following formula:(Fe_(1−a)T_(a))_(100−x−v−z−w)Al_(x)(p_(1−b)Si_(b))_(v)C_(z)B_(w)wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent. This amorphoussoft-magnetic alloy has a temperature difference ΔT_(x) of at least 20 Kin a supercooled liquid.

Preferably, the subscripts a, b, x, v, z, and w satisfy therelationships, 0≦a≦0.15 by atomic ratio, 0.1 by atomic ratio≦b≦0.35 byatomic ratio, 0 atomic percent<x≦15 atomic percent, 8 atomicpercent<v≦18 atomic percent, 0.5 atomic percent≦z≦7.4 atomic percent,and 3 atomic percent≦w≦14 atomic percent. This amorphous soft-magneticalloy has a temperature difference ΔT_(x) of at least 40 K in asupercooled liquid.

More preferably, the subscripts a, b, x, v, z, and w satisfy therelationships, 0≦a≦0.15 by atomic ratio, 0.1 by atomic ratio≦b≦0.28 byatomic ratio, 0 atomic percent<x≦10 atomic percent, 11.3 atomicpercent<v≦14 atomic percent, 1.8 atomic percent≦z≦4.6 atomic percent,and 5.3 atomic percent≦w≦8.6 atomic percent. This amorphoussoft-magnetic alloy has a temperature difference ΔT_(x) of at least 60 Kin a supercooled liquid.

Fe—Al—Ga—C—P—Si—B glassy alloys are known. This glassy alloy containsiron (Fe) and other elements which facilitate the formation of anamorphous phase, such as aluminum (Al), gallium (Ga), carbon (C),phosphorus (P), silicon (Si), and boron (B).

On the other hand, the glassy alloy of the present invention containsFe, Al, C, P, Si, and B. That is, the glassy alloy of the presentinvention does not contain Ga, but does contain an increased amount ofAl. Thus, it is confirmed that the glassy alloy of the present inventioncan contain an amorphous phase regardless of the omission of Ga, whichhas been considered to be an essential element for the formation of theamorphous layer, and that this glassy alloy has a large temperaturedifference ΔT_(x) in a supercooled liquid.

The amorphous soft-magnetic alloy of the present invention exhibits highamorphous formability compared to the conventional Fe—Al—Ga—C—P—Si—Balloy. Since a perfect amorphous phase can be formed at a decreasedcooling rate, a bulk alloy having a relatively large size and containingan amorphous phase can be produced by a casting process.

Since the entire texture is composed of a complete amorphous phase, theamorphous soft-magnetic alloy of the present invention exhibitssignificantly improved permeability and saturation magnetizationcompared to conventional glassy alloys, resulting in superior softmagnetic characteristics.

The internal stress in the amorphous soft-magnetic alloy can be relievedunder an appropriate condition without precipitation of a crystallinephase, and the soft magnetic characteristics are further improved.

Aluminum (Al) is an essential element for the amorphous soft-magneticalloy of the present invention. At an Al content x of 20 atomic percentor less, this alloy has a perfect amorphous phase due to extremelyenhanced amorphous formability of Al, and the amorphous soft-magneticalloy has a temperature difference ΔT_(x) of 20 K or more in asupercooled liquid.

Since Al has a negative enthalpy of mixing with Fe and has an atomicradius which is larger than that of Fe, a combined use of Al with P, B,and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization and can yield a thermally stable amorphous structure.

Moreover, Al raises the Curie temperature of the amorphous soft-magneticalloy and improves thermal stability of various magneticcharacteristics.

The Al content x2 is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x2 exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

Iron (Fe) is essential for the amorphous soft-magnetic alloy of thepresent invention as a magnetic element. The iron (Fe) may be partiallyreplaced with at least one element T selected from Co and Ni. A higherFe content contributes to improved saturation magnetization of theresulting amorphous soft-magnetic alloy.

Carbon (C), phosphorus (P), silicon (Si), and boron (B) are elementshaving amorphous formability. A multicomponent composition includingthese elements, in addition to Fe and Al, facilitates the formation of astable amorphous phase, compared to an Fe—Al binary composition.

In particular, phosphorus (P) having high amorphous formabilityfacilitates the formation of an amorphous phase over the entire textureand the occurrence in a temperature difference ΔT_(x) in a supercooledliquid.

Combined use of P and Si further increases the temperature differenceΔT_(x) in the supercooled liquid and facilitates the formation of alarge bulk alloy composed of a single amorphous phase.

When both phosphorus and silicon are added in combination, the totalcontent v of the phosphorus and silicon is preferably more than 0 to 22atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid and an increased size in abulk alloy composed of a single amorphous phase.

The subscript b representing the relative Si and P contents by atomicratio is preferably in the range of 0≦b≦0.8 when 0 atomic percent<v≦22atomic percent, 0.1≦b≦0.35 when 8 atomic percent≦v≦18 atomic percent, or0.1≦b≦0.28 when 11.3 atomic percent≦v≦14 atomic percent.

When the subscript b exceeds 0.8, an excess amount of Si may undesirablycause disappearance of the temperature difference ΔT_(x) in thesupercooled liquid.

Herein, the Si content in the amorphous soft-magnetic alloy is in therange of preferably 17.6 atomic percent or less, more preferably 0.8 to6.3 atomic percent, and most preferably 1.13 to 3.92 atomic percent.

The above-mentioned ranges for the subscripts b and v representing the Pand Si contents, respectively, contribute to an increased temperaturedifference ΔT_(x) in a supercooled liquid and an increase in size of abulk alloy having a single amorphous phase.

The subscript z representing the C content is in the range of preferablymore than 0 to 12 atomic percent, more preferably 0.5 to 7.4 atomicpercent, and most preferably 1.8 to 4.6 atomic percent.

The subscript w representing the B content is in the range of preferablymore than 0 to 16 atomic percent, more preferably 3 to 14 atomicpercent, and most preferably 5.3 to 8.6 atomic percent.

The amorphous soft-magnetic alloy may contain 4 atomic percent or lessGe, and 0 to 7 atomic percent of at least one element selected from thegroup consisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

The amorphous soft-magnetic alloy of the present invention has atemperature difference ΔT_(x) of at least 35 K in the above compositionor at least 50 K in an optimized composition.

The amorphous soft-magnetic alloy of the present invention may containother incidental impurities.

The amorphous soft-magnetic alloy of the present invention may be formedby a casting process, a single- or twin-roller quenching process, aspinning-in-liquid process, an atomizing process in high-pressure gas,or a casting process of a melt into various shapes, e.g., a bulk, atape, a wire, or a powder. In particular, an amorphous soft-magneticalloy having a thickness and a diameter which are ten or more timesthose of conventional amorphous soft-magnetic alloys can be formed by asingle-roller quenching process, a casting process, or an injectionprocess.

The resulting amorphous soft-magnetic alloy exhibits magnetism at roomtemperature and improved magnetism after annealing. This amorphoussoft-magnetic alloy is applicable to various magnetic articles.

The preferred cooling rate depends on the composition of the alloy, thetype of the cooling process, and the size and shape of the article, andis generally in the range of 1 to 10⁴ K/s. The cooling rate isdetermined so that the glass phase does not contain precipitatedcrystalline phases, such as Fe₃B, Fe₂B, and Fe₃P phases.

As an exemplary process for making the amorphous soft-magnetic alloy, aninjection process using an injection mold will now be described. In thisinjection process, a melt of an amorphous soft-magnetic alloy having theabove composition is injected into a toroidal cavity of a mold through anozzle so that the melt is cooled and solidified in the cavity to form atoroidal article. The melt is injected into the mold along a tangentline of the outer mold surface.

FIGS. 32, 33A and 33B show an injection mold. This mold 121 includes ahollow cylinder 141 formed of a rolled sheet 140, an upper mold 125, anda lower mold 126. The upper mold 125 comes into contact with a partingplane 129, while protuberances 127 of the upper mold 125 engages withrecesses 128 of the lower mold 126 so that the relative position betweenthe upper mold 125 and the lower mold 126 is secured and the hollowcylinder 141 is inserted into a hole 120 passing through the upper mold125.

The parting plane 129 of the lower mold 126 is provided with a shallowcircular recess 122 in the substantial center thereof. The parting plane129 is provided with a sprue 123 and a gate 124 thereon. The sprue 123communicates with the recess 122 and extends along a tangent line of theperipheral wall 122 a of the recess 122, the tangent line being parallelto the recesses 128 of the lower mold 126. The recess 122 and the sprue123 have substantially the same depth. The gate 124 communicates with aside wall of the lower mold 126.

The hollow cylinder 141 is inserted into the hole 120 so that the bottomend 141 a of the hollow cylinder 141 comes into contact with the surface122 b of the recess 122. The peripheral face 141 b of the hollowcylinder 141 and the peripheral wall 122 a of the recess 122 are therebyconcentrically arranged so as to form a toroidal cavity A, as shown inFIG. 33A. Thus, the peripheral wall 122 a of the recess 122 defines theouter diameter of the cavity A, whereas the peripheral face 141 b of thehollow cylinder 141 defines the inner diameter of the cavity A.

As shown in FIG. 32, the hollow cylinder 141 is formed by rolling arectangular sheet 140 so that both ends 142 and 143 thereof overlap. Therolled sheet 140 is inserted into the hole 120 in the upper mold 125 andis supported as the hollow cylinder 141 by the inner wall 120 a of thehole 120. Since, these ends 142 and 143 are not affixed to each other,the diameter of the hollow cylinder 141 is appropriately changeable.Thus, the inner diameter of the cavity A is also changeable.

The rectangular sheet 140 may be formed of any material which is notreactive with the melt of the amorphous soft-magnetic alloy, has amelting point above the temperature (1,000 to 1,400° C.) of the melt,and exhibits high thermal conductivity. Examples of such materialsinclude metal foils of copper (Cu), aluminum (Al), gold (Au), silver(Ag), and platinum (Pt), and carbon sheets. A copper foil is preferred.

It is preferable that the thermal expansion coefficient of the hollowcylinder 141 be the same as that of the amorphous soft-magnetic alloy,since the hollow cylinder 141 similarly expands or shrinks by the heatof melt of the amorphous soft-magnetic alloy injected into the mold.

As shown in FIG. 33A, the peripheral wall 122 a of the cavity A ispartly cut out and communicates with the sprue 123. One side wall of thesprue 123 extends along a tangent line of the peripheral wall 122 a ofthe recess 122, the tangent line being parallel to the recesses 128.

The peripheral wall 122 a is also connected to the other side wall ofthe sprue 123. The other side wall extends along a tangent line of theperipheral face 141 b of the hollow cylinder 141. These two side wallsof the sprue 123 are parallel to each other.

It is preferable that the sprue 123 extends along the tangent line ofthe peripheral wall 122 a of the cavity A. In the present invention, thesprue 123 may slightly shift from the tangent line as long as the sprue123 communicates with the cavity A.

In injection molding using the mold 121, as shown in FIGS. 32 and 33A,the upper mold 125 is engaged with the lower mold 126 and the hollowcylinder 141 is inserted into the hole 120 of the upper mold 125 to formthe cavity A. A nozzle 131 for supplying a melt for an amorphoussoft-magnetic alloy is put into contact with the gate 124. The melt isejected from the nozzle 131 by pressure of an inert gas which issupplied from a gas supply source not shown in the drawings. The ejectedmelt enters the cavity A through the gate 124 and the sprue 123.

Since the sprue 123 extends along the tangent line of the peripheralwall 122 a of the cavity A in a direction parallel to the recesses 128,the ejected melt enters the cavity A along the peripheral wall 122 a inthe Z direction in FIG. 33A without diversion.

The melt is cooled in the sprue 123 and the cavity A and is solidifiedin the cavity A to form a ring. The diameter of the hollow cylinder 141is r₁ before the injection of the melt into the cavity A as shown inFIG. 33A, and decreases to r₂ by the deformation of the hollow cylinder141 due to a reduction in volume during solidification of the melt. Aninjection-molding precursor 151 primarily composed of an amorphous phaseis formed in such a manner, as shown in FIG. 34.

The injection-molding precursor 151 consists of a ring portion 152 and asprue portion 153. The sprue portion 153 is removed to form a ringinjection-molding article 111 of the amorphous soft-magnetic alloy.

In order to prevent clogging in the nozzle 131 due to oxidation of themelt, the injection of the melt into the mold 121 is preferablyperformed in a low-oxygen atmosphere, such as an inert gas or vacuumatmosphere.

The temperature of the melt is in the range of preferably (T_(m)−100) Kto (T_(m)+300) K and more preferably T_(m) K to (T_(m)+100) K, whereinT_(m) indicates the melting point of the amorphous soft-magnetic alloy.At a temperature of less than (T_(m)−100) K, clogging andcrystallization of the melt may in the nozzle 131 occur due to anunstable supercooled state. At a temperature exceeding (T_(m)+300) K, noparticular effects reflecting this temperature are found.

For example, an amorphous soft-magnetic alloy having a composition ofFe₇₀Al₇P_(9.65)C_(3.45)B_(6.9)Si₃ has a melting point of 1,317 K. Thus,the temperature of this melt is preferably in the range of 1,217 to1,617 K and more preferably 1,317 to 1,417 K.

The injection pressure of the melt is in the range of preferably 29 to490 kPa and more preferably 98 to 294 kPa. At an injection pressure ofless than 29 kPa, the entire cavity is not filled with the melt. At aninjection pressure exceeding 490 kPa, the melt may leak from thejunction between the upper mold 125 and the lower mold 126 of the mold121, and stress may remain in the molded article.

Since the amorphous soft-magnetic alloy of the present inventioncontains Fe as a magnetic component and Al, P, C, Si, and B havingamorphous formability, the amorphous alloy exhibits superior softmagnetic characteristics. Since Al has high amorphous formability, theentire texture is amorphous.

Since this amorphous soft-magnetic alloy has a large temperaturedifference ΔT_(x) of at least 20 K in a supercooled liquid, an amorphousphase can be formed from a melt at a relatively low cooling rate. Thus,a bulk alloy which is thicker than a tape can be produced. Inparticular, a bulk cast or injection molding article can be formed by acasting or injection process using a melt of an alloy. The abovedescribed switching power supply, filter, and amplifying device usingthis molded article exhibits superior characteristics.

This amorphous soft-magnetic alloy exhibits high amorphous formabilitycompared to the conventional Fe—Al—Ga—C—P—Si—B alloy. Since a perfectamorphous phase can be formed at a decreased cooling rate, a bulk alloyhaving a relatively large size and containing an amorphous phase can beproduced by a casting process. This homogeneous bulk alloy may bepulverized in order to produce magnetic powder cores.

Since the entire texture is composed of a complete amorphous phase, theamorphous soft-magnetic alloy exhibits significantly improvedpermeability and saturation magnetization, resulting in superior softmagnetic characteristics.

The internal stress in the amorphous soft-magnetic alloy can be relievedunder an appropriate condition without precipitation of a crystallinephase due to the complete amorphous phase, and the soft magneticcharacteristics are further improved.

EXAMPLES Example 1

Properties of Magnetic Powder Core Composed of Glassy Alloy Prepared bySingle-Roller Process

Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B, and Siwere melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare an ingot having a compositionFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃. This ingot was melted in a crucibleand was jetted onto a rotating roller through a nozzle in areduced-pressure Ar atmosphere by a single-roller process to quench themelt and to form a glassy alloy tape with a width of 15 mm and athickness of 20 μm of an amorphous texture. The tape was pulverized inair using a rotor mill and the trituration was classified to selectparticles with diameters of 45 to 150 μm as a glassy alloy powder.

A mixture of 97 parts by weight of glassy alloy powder, 1 part by weightof calcium stearate as an insulating material, and 2 parts by weight ofliquid glass was dried at 473 K (200° C.) for 1 hour in air and wasdisintegrated. The mixture was loaded into a tungsten carbide mold shownin FIG. 2 and was heated from room temperature (298 K or 25° C.) to amolding temperature T_(s) of 573 K (300° C.) or 623 K (350° C.) by apulsed current from an energizing unit under a pressure P_(s) of 600 MPaor 900 MPa using the upper and lower punches 12 and 13, respectively, inthe discharge plasma sintering apparatus of a reduced pressureatmosphere of 6.6×10⁻³ Pa. The mixture was held at the moldingtemperature T_(s) for approximately 8 minutes while maintaining theabove molding pressure P_(s) to complete the compression molding.

The molded article was annealed at an annealing temperature T_(a) of 573(300° C.) to 723 K (450° C.) for 3,600 seconds to produce a requirednumber of toroidal magnetic powder cores with an outer diameter of 12mm, an inner diameter of 6 mm, and a thickness of 2 mm.

Properties of Glassy Alloy Powder

FIG. 4 shows the X-ray diffraction patterns of the powder and the tapeof the glassy alloy having the compositionFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃. As shown in FIG. 4, both the powderand the tape have broad X-ray diffraction patterns which are inherent inamorphous textures. The amorphous phase is maintained afterpulverization of the glassy alloy tape.

FIG. 5 shows differential scanning calorimetric (DSC) thermograms of thepowder and the tape of the above glassy alloy at a heating rate of 40K/min (=0.67 K/sec). According to these DSC thermograms, the glassyalloy tape has a glass transition temperature T_(g) at 760 K and acrystallization temperature T_(x) at 821 K, thus the temperaturedifference ΔT_(x) (=T_(x)−T_(g)) in the supercooled liquid being 61 K.The glassy alloy powder has a glass transition temperature T_(g) at 760K and a crystallization temperature T_(x) at 822 K, thus the temperaturedifference ΔT_(x) being 62 K.

Accordingly, the glassy alloy powder and tape ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ has a broad supercooled-liquid regionbelow the crystallization temperature T_(x), exhibits a largetemperature difference ΔT_(x), and thus has high amorphous formabilityand thermal stability.

Dependence of Magnetic Characteristics on Annealing Temperature (Ta)

FIGS. 6 and 7 show the dependence of magnetic flux density (B_(2.4k))and the coercive force (H_(c)) on the annealing temperature (T_(a)) ofthe magnetic powder cores which are composed of theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder and the insulatingmaterial. In FIGS. 6 and 7, the plot (▪) illustrates the results at amolding temperature T_(s) of 573 K (300° C.) and a molding pressureP_(s) of 900 MPa, the plot (●) illustrates the results at a moldingtemperature T_(s) of 623 K (350° C.) and a molding pressure P_(s) of 600MPa, and the plot (▾) illustrates the results at a molding temperatureT_(s) of 623 K (350° C.) and a molding pressure P_(s) of 900 MPa. In allthe cases, the holding time at the annealing temperature T_(a) was 3,600seconds. The magnetic flux density (B_(2.4k)) in FIG. 6 represents thedensity when a magnetic field of 2.4 kA/m is applied.

Magnetic powder cores for comparison were prepared as in EXAMPLE 1,except that carbonyl iron powder was used instead of theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder.

FIGS. 8 and 9 show the dependence of magnetic flux density (B_(2.4k))and the coercive force (H_(c)) on the annealing temperature (T_(a)) ofthe magnetic powder cores which are composed of the Fe powder and theinsulating material. In FIGS. 8 and 9, the plot (▪) illustrates theresults at a molding temperature T_(s) of 673 K (400° C.) and a moldingpressure P_(s) of 600 MPa, the plot (●) illustrates the results at amolding temperature T_(s) of 623 K (350° C.) and a molding pressureP_(s) of 600 MPa, the plot (▾) illustrates the results at a moldingtemperature T_(s) of 573 K (300° C.) and a molding pressure P_(s) of 900MPa, and the plot (♦) illustrates the results at a molding temperatureT_(s) of 573 K (300° C.) and a molding pressure P_(s) of 600 MPa. In allthe cases, the holding time at the annealing temperature T_(a) was 3,600seconds. The magnetic flux density (B_(2.4k)) in FIG. 8 represents thedensity when a magnetic field of 2.4 kA/m is applied.

FIG. 6 illustrates that the magnetic powder core using theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibits an increased magnetic flux density (B_(2.4k)) afterannealing regardless of the molding conditions, such as the moldingtemperature T_(s) and the molding pressure P_(s). The magnetic fluxdensity (B_(2.4k)) of the annealed magnetic powder core significantlyincreases at an annealing temperature T_(a) above 623 K (350° C.). Onthe other hand, the magnetic flux density (B_(2.4k)) does notsubstantially vary up to an annealing temperature T_(a) of 623 K (350°C.) under the conditions of T_(s)=673 K (400° C.) and P_(s)=600 MPa.

FIG. 7 demonstrates that the magnetic powder core using theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibits a decreased coercive force (Hc) after annealingregardless of the molding conditions. The coercive force (Hc) is 100 A/mor less by annealing at an annealing temperature T_(a) in the range ofapproximately 603 K to 713 K, 80 A/m or less at an annealing temperatureT_(a) in the range of approximately 623 K to 703 K, 40 A/m or less at anannealing temperature T_(a) in the range of approximately 653 K to 703K, and is the minimum of approximately 15 A/m at 693 K (420° C.) andaround.

In contrast, as shown in FIG. 8, the magnetic flux density (B_(2.4k)) ofthe magnetic powder core for comparison does not substantially vary byannealing regardless of the molding conditions including the moldingtemperature T_(s) and the molding pressure P_(s).

As shown in FIG. 9, the coercive force (Hc) of this magnetic powder corefor comparison does also not substantially vary by annealing regardlessof the molding conditions.

Frequency (f) Characteristics of Permeability and Core Loss

FIG. 10 shows the frequency (f) characteristics of the permeability (μ′)of the magnetic powder cores which are composed of theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder and the insulatingmaterial. FIG. 11 shows the frequency (f) characteristics of the coreloss (W) of these magnetic powder cores in which the core loss wasmeasured at a frequency in the range of 10 kHz to 100 kHz and a magneticflux density (Bm) of 0.1 T. In FIGS. 10 and 11, the plot (●) illustratesthe results at a molding temperature T_(s) of 623 K (350° C.), a moldingpressure P_(s) of 600 MPa, and an annealing temperature T_(a) of 693 K(420° C.), and the plot (▾) illustrates the results at a moldingtemperature T_(s) of 623 K (350° C.), a molding pressure P_(s) of 900MPa, and an annealing temperature T_(a) of 683 K (410° C.). In all thecases, the holding time at the annealing temperature T_(a) was 3,600seconds.

FIGS. 12 and 13 show the frequency (f) characteristics of thepermeability (μ′) and the core loss (W) of magnetic powder cores whichwere prepared using a carbonyl iron powder and an insulating materialfor comparison in which the core loss was measured at a frequency in therange of 10 kHz to 100 kHz and a magnetic flux density (Bm) of 0.1 T. InFIGS. 12 and 13, the plot (▪) illustrates the results at a moldingtemperature T_(s) of 673 K (400° C.), a molding pressure P_(s) of 600MPa, and an annealing temperature T_(a) of 673 K (400° C.), the plot (●)illustrates the results at a molding temperature T_(s) of 623 K (350°C.), a molding pressure P_(s) of 600 MPa, and an annealing temperatureT_(a) of 673 K (400° C.), the plot (▾) illustrates the results at amolding temperature T_(s) of 573 K (300° C.), a molding pressure P_(s)of 900 MPa, and an annealing temperature T_(a) of 673 K (400° C.), andthe plot (♦) illustrates the results at a molding temperature T_(s) of573 K (300° C.), a molding pressure P_(s) of 600 MPa, and an annealingtemperature T_(a) of 673 K (400° C.). In all the cases, the holding timeat the annealing temperature T_(a) was 3,600 seconds.

FIG. 10 illustrates that the magnetic powder core using theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibits a constant permeability (μ′) over a broad frequencyrange and a relatively small decrease in the permeability (μ′) in ahigh-frequency region above 1,000 kHz. Thus, this magnetic powder coreexhibits superior frequency (f) characteristics on the permeability (μ′)regardless of the molding conditions, such as the molding temperatureT_(s) and the molding pressure P_(s). The magnetic powder core ●(T_(s)=623 K, P_(s)=600 MPa, and T_(a)=693 K) exhibits a constantpermeability over the broad frequency range of 0.3 to 10,000 kHz, andthe magnetic powder core ♦ (T_(s)=623 K, P_(s)=900 MPa, and T_(a)=683 K)exhibits a constant permeability over the broad frequency range of 0.3to 1,000 kHz. Thus, these magnetic powder cores are preferablyapplicable to magnetic core components requiring a constant permeabilityup to a high frequency region, such as transformer cores for switchingpower supplies and smoothing choke cores.

In contrast, as shown in FIG. 12, the magnetic powder cores forcomparison have a narrower constant permeability region compared to themagnetic powder cores of EXAMPLE 1. In the magnetic powder core ▪(T_(s)=673 K, P_(s)=600 MPa, and T_(a)=673 K), the permeabilitysignificantly decreases as the frequency increases. In the magneticpowder core ● (T_(s)=623 K, P_(s)=600 MPa, and T_(a)=673 K), thepermeability significantly decreases at a frequency above 10 kHz. In themagnetic powder cores ▾ (T_(s)=573 K, P_(s)=900 MPa, and T_(a)=673 K)and ♦ (T_(s)=573 K, P_(s)=600 MPa, and T_(a)=673 K), the permeabilitysignificantly decreases at a frequency region above 200 kHz. Thesemagnetic powder cores exhibit permeabilities which are lower than thoseof the magnetic powder cores of EXAMPLE 1 in a high-frequency region of1,000 kHz or more.

FIGS. 11 and 13 show that the magnetic powder cores using theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibit lower core loss compared to the magnetic powder coresin the frequency region of 10 kHz to 100 kHz. The core loss of themagnetic powder cores of the present invention is one order of magnitudesmaller than the core loss of the magnetic powder cores for comparisonin the frequency region of 10 kHz to 20 kHz. Accordingly, the magneticpowder core of the present invention exhibits low core loss from alow-frequency region to a high-frequency region.

Dependence of Physical Properties on C, P, Si, and B Contents in GlassyAlloy

Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B, and Siwere melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare ingots represented the formulaFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w). Each ingot was melted in acrucible and was jetted onto a rotating roller through a nozzle in areduced-pressure Ar atmosphere by a single-roller process to quench themelt and to form a glassy alloy tape with a width of 1 mm and athickness of 20 μm of an amorphous texture. The resulting glassy alloyshad the following compositions:Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(5.75)B_(4.6),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(8.05)B_(4.6),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(5.75)B_(6.9),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.45)B_(6.9),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(3.45)B_(4.6),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(5.75)B_(2.3),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(8.05)B_(2.3),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(3.45)B9.2,Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(1.15)B_(9.2),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(1.15)B_(6.9),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(4.6)B_(5.75),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(4.6)B_(6.9),Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(3.45)B_(8.05),andFe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(2.3)B_(0.05),

Each glassy alloy tape was subjected to DSC at a heating rate of 0.67K/sec to determine the glass transition temperature T_(g), thecrystallization temperature T_(x), and thus the temperature differenceΔT_(x) in the supercooled liquid.

FIGS. 14, 15, and 16 show the dependence of the glass transitiontemperature T_(g), the crystallization temperature T_(x), and thetemperature difference ΔT_(x) in the supercooled liquid, respectively,on the composition of the glassy alloy.

Numbers near the corresponding plots in the ternary diagrams shown inFIGS. 14, 15, and 16 indicate the glass transition temperature T_(g),the crystallization temperature T_(x), and the temperature differenceΔT_(x) in the supercooled liquid, respectively. Numbers on isothermallines in FIGS. 14 to 16 indicate the temperatures of the isothermallines.

FIG. 14 shows that the glass transition temperature T_(g) increases withan increased B content or a decreased C content. The isothermal line atT_(g)=760 K lies in the range of a B content w of 4.1 to 8.05 atomicpercent and a C content z of 2.3 to 5.1 atomic percent.

FIG. 15 shows that the crystallization temperature T_(x) also increaseswith an increased B content or a decreased C content. The isothermalline at T_(x)=815 K lies in the range of a B content w of 4 to 8.4atomic percent and a C content z of 0.3 to 5 atomic percent.

FIG. 16 shows that the region surrounded by the isothermal line atTg=760 K shown in FIG. 14 and the isothermal line at T_(x)=815 K shownin FIG. 15 corresponds to the region surrounded by the isothermal lineat ΔT_(x)=60 K. The temperature difference ΔT_(x) in the supercooledliquid exceeds 60 K within this range. In particular, the temperaturedifference ΔT_(x) of theFe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.45)B_(6.9) glassy alloy is 63 K.

Example 2

Properties of Magnetic Powder Core Composed of Glassy Alloy Prepared byGas Atomizing Process

Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B, and Siwere melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare an ingot having a compositionFe₇₇Al₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87). This ingot was melted in acrucible provided with an atomizing nozzle at 1,350° C. (which was atleast 140° C. higher than the melting point of the glassy alloy). Themelt was atomized together with gaseous argon with a pressure of 8.6 MPathrough the atomizing nozzle to prepare an alloy powder. The alloypowder was classified into several powders having various particle sizeranges.

A mixture of 97 parts by weight of each glassy alloy powder, 1 parts byweight of calcium stearate as an insulating material, and 2 parts byweight of liquid glass was prepared. The mixture was dried in anatmosphere at 473 K (200° C.) for 1 hour and was disintegrated. Themixture was loaded into a tungsten carbide mold shown in FIG. 2 and washeated from room temperature (298 K or 25° C.) to a molding temperatureT_(s) of 623 K (350° C.) by a pulsed current from an energizing unitunder a pressure P_(s) of 1,000 MPa using the upper and lower punches 12and 13, respectively, in the discharge plasma sintering apparatus of areduced pressure atmosphere of 6.6×10⁻³ Pa. The mixture was held at themolding temperature T_(s) for approximately 8 minutes while maintainingthe above molding pressure P_(s) to complete the compression molding.

The molded article was annealed at an annealing temperature T_(a) of 683(410° C.) for 3,600 seconds to produce a required number of toroidalmagnetic powder cores with an outer diameter of 12 mm, an inner diameterof 6 mm, and a thickness of 2 mm.

Permeability and DC Superposition Characteristic of Magnetic Powder Core

The permeability and the DC superposition characteristics of magneticpowders cores were measured. In each magnetic powder core, the amorphousvolume fraction Vamo in the texture was 93% or 98% and the particle sizewas 38 μm or less. The amorphous volume fraction Vamo was determined byDSC.

FIGS. 17A and 17B show the dependence of the effective permeability (λ′)and the rate (Δμ′) of change in permeability, respectively, of thesemagnetic powder cores on the magnetic field. In these drawings, the plot(●) indicates an amorphous volume fraction of 93%, and the plot (▾)indicates an amorphous volume fraction of 98%. FIG. 17B also shows therate (Δμ′) of change in permeability of a magnetic powder core usingcarbonyl iron powder (COMPARATIVE EXAMPLE).

FIGS. 17A and 17B illustrate that the permeability and the rate ofchange in permeability of the magnetic powder cores according to thepresent invention do not substantially depend on the magnetic field.Thus, the magnetic powder cores of the present invention exhibit stablesoft magnetic characteristics. Moreover, the soft magneticcharacteristics are not affected by the amorphous volume fraction.

Thus, these magnetic powder cores are preferably applicable to magneticcore components requiring a constant permeability, such as transformercores for switching power supplies and smoothing choke cores.

In contrast, in the magnetic powder core of COMPARATIVE EXAMPLE, therate (Δμ′) of change in permeability increases as the magnetic fieldincreases. Since this magnetic powder core exhibits large variations insoft magnetic characteristics, magnetic components, such astransformers, using this magnetic powder core will exhibit inferiorcharacteristics.

FIGS. 18A and 18B illustrate the dependence of the inductance (L) andthe rate of change therein (ΔL) (so-called DC superpositioncharacteristic), respectively, on the DC bias magnetic field (H_(dc)) ofeach magnetic powder core. In these drawings, the plot (●) indicates anamorphous volume fraction of 93%, and the plot (▾) indicates anamorphous volume fraction of 98%. FIG. 18B also shows the rate (ΔL) ofchange in inductance of a magnetic powder core using an FeAlSi amorphousalloy powder (COMPARATIVE EXAMPLE).

FIGS. 18A and 18B illustrate that the inductance (L) and the rate (ΔL)of change in inductance of the magnetic powder cores according to thepresent invention show small changes when the DC bias magnetic field isvaried. Thus, the magnetic powder cores of the present invention exhibitstable soft magnetic characteristics. Moreover, the rate (ΔL) of changedecreases only to approximately −25% in a DC bias magnetic field of6,800 A/m, showing a superior soft magnetic characteristic.

Thus, these magnetic powder cores are preferably applicable to magneticcore components requiring a constant permeability, such as transformercores for switching power supplies and smoothing choke cores.

In contrast, in the magnetic powder core of COMPARATIVE EXAMPLE, therate (ΔL) of change in inductance decreases to approximately −70% whenthe DC bias magnetic field is 6,800 A/m, showing a large variation inmagnetic characteristics. Thus, magnetic components, such astransformers, using this magnetic powder core will exhibit inferiorcharacteristics.

Permeability and Core Loss of Magnetic Powder Core

The permeability and the core loss of three magnetic powders cores weremeasured. These magnetic powder cores were composed of glassy alloypowders having different particle sizes in the range of 38 μm or less,the range of more than 38 μm to 60 μm, and the range of more than 60 μmto 100 μm. The amorphous volume fraction Vamo of each glassy alloy wasdetermined by DSC.

FIGS. 19A, 19B, and 19C illustrate the dependence of the permeability(μ′), the core loss (W_(0.5/200k)) and the core loss (W_(1/100k)),respectively, on the amorphous volume fraction of magnetic powder corescomposed of glassy alloy powders, each having a particle size in therange of more than 60 μm to 100 μm (points ▪), more than 38 μm to 60 μm(points ●), and 38 μm or less (points ▾).

FIG. 19A illustrates that the effective permeability of the magneticpowder core tends to increase as the amorphous volume fraction increasesand that the amorphous volume fraction increases as the particle size ofthe glassy alloy powder decreases.

FIG. 19B shows the core loss (W_(0.5/200k)) which was measured at afrequency of 200 kHz and a saturation magnetic flux density of 0.05 T,and FIG. 19C shows the core loss (W_(1/100k)) which was measured at afrequency of 100 kHz and a saturation magnetic flux density of 0.1 T.

As shown in FIGS. 19B and 19C, the core losses (W_(0.5/200k),W_(1/100k)) of the magnetic powder core tends to increase with anincrease in the amorphous volume fraction, as in the effectivepermeability. Some magnetic powder cores having an amorphous volumefraction exceeding 85% exhibit a core loss (W_(1/100k)) of 700 kW/m³ orless.

Accordingly, it is preferable to use a glassy alloy powder having aparticle size of 38 μm or less in order to obtain a magnetic powder coreexhibiting superior effective permeability and core loss when the glassyalloy powder is prepared by a gas atomizing process. If a glassy alloypowder having a particle size exceeding 38 μm is used, it is preferablethat the particle size be smaller and the amorphous volume fraction belarger.

In particular, a core loss (W_(1/100k)) of the magnetic powder core of700 kW/m³ or less is achieved by an amorphous volume fraction of 85% ormore in the glassy alloy powder, and a core loss (W_(1/100k)) of 400kW/m³ or less is achieved by a particle size of 38 μm or less in theglassy alloy powder.

Example 3

Properties of Magnetic Powder Core Containing Silicone Rubber asInsulating Material

Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B, and Siwere melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare an ingot having a compositionFe₇₇Al₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87). This ingot was melted in acrucible provided with an atomizing nozzle at 1,350° C. (which was atleast 140° C. higher than the melting point of the glassy alloy). Themelt was atomized together with gaseous argon with a pressure of 8.6 MPathrough the atomizing nozzle to prepare an alloy powder. The alloypowder was classified to prepare a glassy alloy powder having a particlesize of 62 μm or less.

Next, the glassy alloy powder was compounded with 0.67 to 4 weight %silicone rubber as an insulating material. The mixture was compressed toa molding pressure P_(s) of 1,500 MPa at room temperature (298 K (25°C.)) in a reduced pressure atmosphere of 6.6×10⁻³ Pa. The compressedmixture was annealed at 683 K (410° C.) for approximately 60 minutesunder this molding pressure P_(s). Magnetic powder cores (EXAMPLES 3-1to 3-5) were prepared in such a manner. These magnetic powder cores weretoroidal with an outer diameter of 12 mm, an inner diameter of 6 mm, anda thickness of 2 mm.

Also, magnetic powder cores for comparison (COMPARATIVE EXAMPLES 3-1 and3-2) were prepared as in the above process but epoxy resin and polyimideresin were used as insulating materials, instead of the silicone rubber.

The core loss (W_(1/100k)) of each magnetic powder core was measured ata frequency of 100 kHz and a saturation magnetic flux density of 0.01 T.Table 1 shows these results.

TABLE 1 Insulating Material Core Loss Content (W_(1/100k)) Type (weight%) (kW/m³) EXAMPLE 3-1 Silicone Rubber 0.67 310 EXAMPLE 3-2 SiliconeRubber 1.33 290 EXAMPLE 3-3 Silicone Rubber 2.0 230 EXAMPLE 3-4 SiliconeRubber 3.0 ≦200 EXAMPLE 3-5 Silicone Rubber 4.0 300 COMPARATIVE EpoxyResin 2.0 620 EXAMPLE 3-1 COMPARATIVE Polyimide Resin 2.0 ≧2,000 EXAMPLE3-2

Table 1 shows that all the magnetic powder cores of EXAMPLES 3-1 to 3-5using the silicone rubber as the insulating material exhibit a core loss(W_(1/100k)) of 310 kW/m³ or less, which is significantly lower thanthat of a conventional magnetic powder core. In particular, the magneticpowder core containing 3 weight % silicone rubber exhibits asignificantly low core loss of 200 kW/m³ or less.

The observed magnetostriction constants of the glassy alloys of EXAMPLES3-1 to 3-5 are in the range of 2×10⁻⁵ to 3×10⁻⁵, demonstrating extremelyreduced internal stress in the magnetic powder cores.

In the magnetic powder cores of COMPARATIVE EXAMPLES 3-1 and 3-2, thecore loss (W_(1/100k)) is higher than that of EXAMPLES 3-1 to 3-5. Inparticular, the magnetic powder core of COMPARATIVE EXAMPLE 3-2 usingthe polyimide insulating material exhibits a core loss (W_(1/100k)) of2,000 kW/m³ or more.

It is considered that the small core loss (W_(1/100k)) in the magneticpowder cores of EXAMPLES 3-1 to 3-5 is caused by small residual stressin the glassy alloy powder due to small hardening stress of the siliconerubber. In contrast, the large core loss (W_(1/100k)) of the magneticpowder cores of COMPARATIVE EXAMPLES 3-1 and 3-2 is considered to becaused by large internal stress due to large hardening stress, sincethese insulating materials are less elastic. In COMPARATIVE EXAMPLE 3-2,it is considered that the extremely large core loss is caused by theaccumulated internal stress due to significantly large hardening stressof the polyimide resin.

Accordingly, a magnetic powder core having extremely small core loss isobtainable by compaction molding of a glassy alloy powder, which isprepared by a gas atomizing process, and a silicone rubber at roomtemperature and annealing of the molded article.

As described above, the magnetic powder core of the present invention isa molded article of a mixture of a glassy alloy powder and an insulatingmaterial, and the glassy alloy powder has a texture primarily composedof an amorphous phase and has a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature. Theinsulating material enhances the resistivity of the entire magneticpowder core and reduces core loss of the magnetic powder core due toreduced eddy current loss. Thus, a reduction in permeability can bemoderated in a high-frequency region.

A magnetic powder core using a glassy alloy having a resistivity of atleast 1.5 μΩ.m exhibits lower core loss in a high-frequency region dueto reduced eddy current loss in the glassy alloy particles.

In the method for making the magnetic powder core of the presentinvention, a magnetic core precursor is annealed at a temperature in therange between (T_(g)−170) K and T_(g) K. Thus, the internal stress ofthe magnetic core precursor is relieved without crystallization of theglassy alloy. Accordingly, a magnetic powder core having low coerciveforce can be produced by the method in accordance with the presentinvention.

Example 4

Heat Dissipation of Step-down Converter Circuit

A toroidal magnetic powder core composed of a glassy alloy having acomposition Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ was prepared as in Example1, except that the molding pressure was 1,500 MPa and the moldingtemperature was room temperature (25° C. (298 K)). The magnetic powdercore had an outer diameter of 18 mm, an inner diameter of 12 mm, and athickness of 5 mm.

A coil was wound by seven turns around the magnetic powder core toprepare a choking coil having an inductance of 2.9 μH.

This choking coil was used as a coil with a magnetic core to mount intoa step-down converter circuit shown in FIG. 24 (EXAMPLE 4). Thisconverter circuit had a transistor switching element, a dioderectification element, and an electrolytic capacitor with anelectrostatic capacitance of 33 μF. The input was a DC of 12 V, theoutput was a DC of 5 V and 25 A, and the switching frequency of theswitching element was 100 kHz. The heat dissipation of the choking coilwas measured. Table 2 shows the results.

Also, step-down converter circuits were assembled using a choking coilsincluding a magnetic powder core of carbonyl iron powder (COMPARATIVEEXAMPLE 4-1) and a magnetic powder core of an FeAlSi alloy (COMPARATIVEEXAMPLE 4-2) as in EXAMPLE 4 to measure the heat dissipation of thechoking coil. Table 2 also shows the result.

TABLE 2 Heat Dissipation (W) EXAMPLE 4 0.5 COMPARATIVE EXAMPLE 4-1 3.9COMPARATIVE EXAMPLE 4-2 1.1

As shown in Table 2, the choking coil of EXAMPLE 4 exhibits lower heatdissipation compared to the choking coils of COMPARATIVE EXAMPLES 4-1and 4-2. Accordingly, the step-down converter circuit using this chokingcoil exhibits high conversion efficiency due to reduced heat dissipationand low loss. Also, the magnetic core of EXAMPLE 2 will showsubstantially the same effect when it is used in the step-down convertercircuit.

As described above, the switching power supply of the present inventionincludes a transformer having a magnetic core composed of a glassy alloypowder. The internal stress of the magnetic core can be relieved byannealing at a temperature which is sufficiently lower than thecrystallization temperature of the glassy alloy, and the heatdissipation from the entire switching power supply can be reduced due toreduced core loss.

The switching power supply of the present invention includes a coil witha magnetic core composed of a glassy alloy powder. The internal stressof the magnetic core can be relieved by annealing at a temperature whichis sufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire switching power supplycan be reduced due to reduced core loss.

Each of the step-down converter circuit, boosting converter circuit, andpolarity-reversing converter circuit of the present invention uses acoil with a magnetic core composed of a glassy alloy powder. Theinternal stress of the magnetic core can be relieved by annealing at atemperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the heat dissipation from theentire converter circuit can be reduced due to reduced core loss.

The active filter of the present invention uses a coil with a magneticcore composed of a glassy alloy powder in the converter circuit therein.Since this magnetic core exhibits low loss, the heat dissipation fromthe entire active filter can be reduced.

The magnetic core exhibiting low permeability does not require a gap forpreventing magnetic saturation, and does not generate a leakage magneticfield which adversely affects other peripheral circuits.

Example 5

Magnetic Characteristics of Glassy Alloy

A glassy alloy powder having a compositionFe₇₇Al₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87) was prepared as in EXAMPLE 4. Amixture of 97 parts by weight of glassy alloy powder and 3 part byweight of silicone elastomer as an insulating material was dried at 473K (200° C.) for 1 hour in air and was disintegrated. The mixture wasloaded into a tungsten carbide mold and was heated to a temperature of683 K under a pressure of 1,500 MPa in the discharge plasma sinteringapparatus of a reduced pressure atmosphere of 6.6×10⁻³ Pa. A toroidalmagnetic powder core with an outer diameter of 12 mm, an inner diameterof 6 mm, and a thickness of 2 mm was thereby prepared. The rate ofchange in amplitude permeability (Δμ′) and the core loss (W) of themagnetic powder core were measured (EXAMPLE 5). The results are shown inFIGS. 35 and 36.

The rate of change in amplitude permeability (Δμ′) and the core loss (W)of a magnetic powder core of carbonyl iron powder were also measured(COMPARATIVE EXAMPLE 5). The results are shown in FIGS. 35 and 36.

FIG. 36 shows the relationship between the rate of change in amplitudepermeability (Δμ′) relative to the amplitude permeability in a magneticfield of 200 A/m and the magnetic field. The magnetic core of EXAMPLE 5exhibits a rate of change in amplitude permeability of approximately −5%in a magnetic field of 2,000 A/m, that is, exhibits substantially thesame amplitude permeability regardless of the magnetic field.

In contrast, the magnetic core of COMPARATIVE EXAMPLE 5 exhibits a rateof change in amplitude permeability exceeding +5% in a magnetic field of2,000 A/m, that is, exhibits a significant change in amplitudepermeability with a change in magnetic field.

FIG. 35 shows the dependence of the core loss (W) measured at a magneticflux density Bm of 0.1 T on the frequency. The magnetic core of presentinvention exhibits a relatively small core loss (W) of approximately 10kWm⁻³ at a frequency of 10 kHz, and a core loss (W) of approximately 250kWm⁻³.

In contrast, the magnetic core of COMPARATIVE EXAMPLE 5 exhibits aconsiderably high core loss (W) of 250 kWm⁻³ at a frequency of 10 kHz,520 kWm⁻³ at a frequency of 20 kHz, and 2,000 kWm⁻³ at a frequency of100 kHz (not shown in the drawing).

The magnetic core composed of the glassy alloy according to the presentinvention exhibits smaller core loss compared to the conventionalcarbonyl iron powder magnetic core and exhibits constant amplitudepermeability over a wide range of magnetic field.

When the magnetic core of the present invention is used as a magneticcore of a filter, the filter exhibits reduced loss and reduced heatdissipation, and outputs smoothed waveforms with less distortion.

As described above, the filter of the present invention includes acapacitor and an inductor of a coil wound around a magnetic core. Themagnetic core is composed of a glassy alloy powder having a temperaturedifference ΔT_(x) in a supercooled liquid and an insulating material.The internal stress of the glassy alloy can be relieved by annealing ata temperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the magnetic core exhibits low coreloss and a substantially constant amplitude permeability over a wideintensity range of magnetic field. Thus, the filter exhibits reducedheat dissipation and outputs less distorted waveforms.

Since a glassy alloy having a resistivity of at least 1.5 μΩ.m is used,the resulting magnetic core shows further reduced core loss due toreduced eddy current loss in the glassy alloy particles in ahigh-frequency region. Accordingly, the filter exhibits furtherdecreased loss.

Moreover, the insulating material increases the resistivity of themagnetic core, resulting in decreased core loss due to reduced eddycurrent loss. Moreover, a reduction in permeability in a high-frequencyregion is suppressed. Thus, the filter exhibits improved high-frequencycharacteristics.

Since the rate of change in amplitude permeability of the magnetic corein a magnetic field of 2,000 A/m is within ±10% of an amplitudepermeability in a magnetic field of 200 A/m, the filter outputs lessdistorted waveforms. Thus, the filter is preferably applicable to asmoothing circuit of a pulse width modulating amplifier.

Since the permeability of the magnetic core at 100 kHz is in the rangeof 50 to 200, the number of turns of the coil can be reduced, resultingin miniaturization of the inductor and thus the filter.

The magnetic core of the filter of the present invention is composed ofa glassy alloy having a predetermined composition, exhibits smaller coreloss compared with a conventional carbonyl iron powder magnetic core,and exhibits constant amplitude permeability over a wide intensity rangeof magnetic field. Thus, the filter exhibits reduced heat dissipationdue to reduced loss and outputs smoothed waveforms with less distortion.

The amplifying device of the present invention includes an amplifier foroutputting a pulsed current and a filter, for smoothing the pulsedcurrent, in connection with the output side of the amplifier. The filterincludes a capacitor and an inductor of coil wound around the magneticcore. Thus, the amplifying device exhibits reduced heat dissipation dueto low loss and outputs waveforms with less distortion.

Example 6

Dependence of Physical and Magnetic Properties on P, Si, C, and BContents

Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B, and Siwere melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare ingots having differentcompositions. Each ingot was melted in a crucible and was jetted onto arotating roller through a nozzle in a reduced-pressure Ar atmosphere bya single-roller process to quench the melt and to form a glassy alloytape, of an amorphous texture, with a width of 1 mm and a thickness of20 μm. Amorphous soft-magnetic alloy tapes of EXAMPLES 6-1 to 6-14 wereprepared in such a manner.

A Ga-containing amorphous soft-magnetic alloy tape represented byFe₇₀Al₅Ga₂P_(9.65)C_(5.75)B_(4.6)Si₃ was prepared for comparison(COMPARATIVE EXAMPLE 6).

Table 3 shows the compositions of the resulting amorphous soft-magneticalloy tapes of the present invention. The compositions are representedby Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w), wherein v is in the rangeof 10.35 to 14.95 atomic percent, Z is in the range of 1.15 to 8.05atomic percent, and w is in the range of 2.3 to 9.2 atomic percent.

The amorphous soft-magnetic alloys of EXAMPLES 6-1 to 6-14 weresubjected to crystallographic analysis by X-ray diffractometry. FIG. 37shows the results.

The amorphous soft-magnetic alloys of EXAMPLES 6-4 and 6-14 andCOMPARATIVE EXAMPLE 6 were subjected to DSC at a heating rate of 0.67K/sec. FIG. 38 and Table 4 show the DSC results.

TABLE 3 Alloy Composition EXAMPLE 6-1Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(5.75)B_(4.6) EXAMPLE 6-2Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(8.05)B_(4.6) EXAMPLE 6-3Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(5.75)B_(6.9) EXAMPLE 6-4Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.45)B_(6.9) EXAMPLE 6-5Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(3.45)B_(4.6) EXAMPLE 6-6Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(5.75)B_(2.3) EXAMPLE 6-7Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(8.05)B_(2.3) EXAMPLE 6-8Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(3.45)B_(9.2) EXAMPLE 6-9Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(1.15)B_(9.2) EXAMPLE 6-10Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(1.15)B_(6.9) EXAMPLE 6-11Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(4.6)B_(5.75) EXAMPLE 6-12Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(4.6)B_(6.9) EXAMPLE 6-13Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(3.45)B_(8.05) EXAMPLE 6-14Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(2.3)B_(8.05)

TABLE 4 T_(g) (K) T_(x) (K) ΔT_(x) (K) EXAMPLE 6-4 758 821 63 EXAMPLE6-14 760 821 61 COMPARATIVE 740 800 60 EXAMPLE 6

FIG. 37 demonstrates that the amorphous soft-magnetic alloy tapes ofEXAMPLES 6-1 to 6-14 exhibit broad X-ray diffraction patterns which areassigned to amorphous textures.

FIG. 38 and Table 4 demonstrate that the amorphous soft-magnetic alloyof EXAMPLE 6-4 has a glass transition temperature T_(g) at 758 K and acrystallization temperature T_(x) at 821 K, thus the temperaturedifference ΔT_(x), represented by ΔT_(x)=T_(x)−T_(g), in the supercooledliquid being 63 K. The amorphous soft-magnetic alloy of EXAMPLE 6-14 hasa glass transition temperature T_(g) of 760 K and a crystallizationtemperature T_(x) of 821° C., thus the temperature difference ΔT_(x),represented by ΔT_(x)=T_(x)−T_(g), in the supercooled liquid being 60 K.

The amorphous soft-magnetic alloy of COMPARATIVE EXAMPLE 6 has a glasstransition temperature T_(g) at 740 K and a crystallization temperatureT_(x) at 800 K, thus the temperature difference ΔT_(x), represented byΔT_(x)=T_(x)−T_(g), in the supercooled liquid being 60 K.

The amorphous soft-magnetic alloys of EXAMPLES 6-4 and 6-14 have each awide supercooled liquid region below the crystallization temperatureT_(x) regardless of the Ga-free composition and a largeΔT_(x)(=T_(x)−T_(g)) as a glassy alloy. Thus, the alloy consisting ofFe, Al, P, C, B, and Si has a large temperature difference ΔT_(x) of atleast 20 K in a supercooled liquid.

The amorphous soft-magnetic alloy tapes of EXAMPLES 6-1 to 6-14 weresubjected to DSC at a heating rate of 0.67 K/sec to measure the glasstransition temperature T_(g), the crystallization temperature T_(x), theCurie temperature T_(c), and the melting point T_(m) and to determinethe temperature difference ΔT_(x) in a supercooled liquid and the ratioT_(g)/T_(m).

FIG. 39 shows the dependence of the glass transition temperature T_(g)on the composition, FIG. 40 shows the dependence of the crystallizationtemperature T_(x) on the composition, FIG. 41 shows the dependence ofthe temperature difference ΔT_(x) in a supercooled liquid on thecomposition, FIG. 42 shows the dependence of the melting point T_(m) onthe composition, FIG. 43 shows the dependence of the ratio T_(g)/T_(m)on the composition, and FIG. 44 shows the dependence of the Curietemperature T_(c) on the composition.

The saturation magnetization (σs) by a VSM (vibrating samplemagnetometer) and the permeability (μe) and coercive force (Hc) by a BHloop tracer were measured for the amorphous soft-magnetic alloy tapes ofEXAMPLES 6-1 to 6-14.

FIG. 45 shows the dependence of the saturation magnetization (σs) on thecomposition, FIG. 46 shows the dependence of the permeability (μe) onthe composition, and FIG. 47 shows the dependence of the coercive force(Hc) on the composition.

Figures attached to the plots in the ternary diagrams in FIGS. 39 to 47represent the glass transition temperature T_(g), the crystallizationtemperature T_(x), the temperature difference ΔT_(x) in the supercooledliquid, melting point T_(m), the ratio T_(g)/T_(m), the Curie pointT_(c), the saturation magnetization (σs), the permeability (μe), and thecoercive force (Hc), respectively.

In FIGS. 39 to 47, a figure shown in the vicinity of each isothermalline or isoline represents the temperature or the value thereof.

FIG. 39 illustrates that the glass transition temperature T_(g)increases with an increased B content and a decreased C content. Theisothermal line at T_(g)=760 K lies in a region defined by the B contentw in the range of 4.1 atomic percent to 8.05 atomic percent and by the Ccontent z in the range of 2.3 atomic percent to 5.1 atomic percent.

FIG. 40 illustrates the crystallization temperature T_(x) increases withan increased B content and a decreased C content, as in the T_(g). Theisothermal line at T_(x)=815 K lies in a region defined by the B contentw in the range of 4 atomic percent to 8.4 atomic percent and by the Ccontent z in the range of 0.3 atomic percent to 5 atomic percent.

As shown in FIG. 41, the region surrounded by the isothermal line atT_(g)=760 K shown in FIG. 39 and the isothermal line at T_(x)=815 Kcorresponds to the isothermal line at ΔT_(x)=60 K. The temperaturedifference ΔT_(x) in the supercooled liquid exceeds 60 K within thisrange. In particular, the amorphous soft-magnetic alloyFe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.45)B_(6.9) of EXAMPLE 6-4exhibits a temperature difference ΔT_(x) of 63 K.

FIG. 42 illustrates that the melting point T_(m) exhibits the maximum of1,361 K at a higher-B-content side and the minimum of 1,226 K at alower-B-content side of the isothermal line at 1,290 K. Since thedifference between the maximum and the minimum is 135 K, the meltingpoint T_(m) of this amorphous soft-magnetic alloy is sensitive to the Bcontent w.

With reference to FIG. 43, the high sensitivity of the melting pointT_(m) to the composition affects the dependence of the ratio T_(g)/T_(m)on the composition. The ratio T_(g)/T_(m) slightly increases alower-B-content side of the isoline at T_(g)/T_(m)=0.6, which lies alonga B content of 5.75 atomic percent. A large ratio T_(g)/T_(m) means adecreased temperature difference ΔT_(x) between the melting point T_(m)and the glass transition temperature T_(g). Thus, an alloy having acomposition within this range has enhanced amorphous formability eventhe cooling rate is decreased; that is, the critical cooling rate islow. Accordingly, the larger T_(g)/T_(m), the higher amorphousformability.

Comparing FIG. 43 with FIG. 41, the region of T_(g)/T_(m) of 0.60 orless in FIG. 43 overlaps with the region of ΔT_(x) of 60 K or more inFIG. 41. Thus, a high T_(g)/T_(m) region does not always overlap with ahigh ΔT_(x) region. The T_(g)/T_(m), however, is as relatively high as0.57 to 0.58 even in a region of ΔT_(x) of 60 K or more. Thus, thisamorphous soft-magnetic alloy within this range exhibits relatively highamorphous formability.

FIG. 44 illustrates that the Curie temperature T_(c) increases with adecreased total content of P and Si. FIG. 45 illustrates that thesaturation magnetization (σs) also increases with a decreased totalcontent of P and Si. At a total content of 12.65 atomic percent or less,the saturation magnetization (σs) is 180×10⁻⁶ (Wb.m.kg⁻¹) or more. At atotal content of 11.5 atomic percent or less, the saturationmagnetization (σs) is 190×10⁻⁶ (Wb.m.kg⁻¹) or more. Thus, the amorphoussoft-magnetic alloy of the present invention exhibits a high saturationmagnetization (σs).

As described above, the Curie temperature T_(c) is highly correlatedwith the saturation magnetization (σs). Accordingly, an optimizedcomposition increases both the Curie temperature T_(c) and thesaturation magnetization (σs) and the resulting amorphous soft-magneticalloy exhibits high thermal stability of magnetic characteristics due tothe increased Curie temperature T_(c).

FIG. 46 shows a maximum permeability (μe) of 28,300, but does not shownor suggest a clear relationship between the composition and thepermeability (μe). Thus, it is considered that the dependence of thepermeability (μe) on the P, C, B, and Si contents is not significant.

FIG. 47 illustrates that the coercive force (Hc) does not show a cleardependence on the P, C, B, and Si contents, unlike the saturationmagnetization (σs) and the above thermal properties.

Accordingly, the thermal properties T_(g), T_(x), ΔT_(x), T_(m),T_(g)/T_(m), T_(c) and the saturation magnetization (σs) show highdependence on the P, C, B, and Si contents.

Example 7

Dependence of Physical and Magnetic Properties on Fe and Al Contents

Melts prepared by melting ingots having different composition weresprayed onto a rotating roller in a reduced-pressure atmosphere as inEXAMPLE 6 to prepare amorphous soft-magnetic alloy tapes with a width of1 mm and a thickness of 20 μm of EXAMPLES 7-15 to 7-18. These amorphoussoft-magnetic alloys had compositions represented byFe_(100−x−y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))_(y) wherein x was 1to 5 atomic percent and y was 18 to 22 atomic percent. Table 5 shows thecompositions of the resulting amorphous soft-magnetic alloy tapes. FIG.48 illustrates X-ray diffraction patterns of the resulting amorphoussoft-magnetic alloy.

TABLE 5 Alloy Composition EXAMPLE 7-15Fe₇₇Al₅(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))₁₈ EXAMPLE 7-16Fe₇₇Al₃(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))₂₀ EXAMPLE 7-17Fe₇₇Al₁(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))₂₂ EXAMPLE 7-18Fe₇₉Al₁(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))₂₀

FIG. 48 demonstrates that the amorphous soft-magnetic alloy tapes ofEXAMPLES 7-15 to 7-18 exhibit broad X-ray diffraction patterns which areassigned to amorphous textures.

The amorphous soft-magnetic alloy tapes of EXAMPLES 7-15 to 7-18 weresubjected to DSC at a heating rate of 0.67 K/sec to determine the glasstransition temperature T_(g), the crystallization temperature T_(x), theCurie temperature T_(c), and the melting point T_(m), the temperaturedifference ΔT_(x) in a supercooled liquid, and the ratio T_(g)/T_(m).

FIG. 49 shows the dependence of the glass transition temperature T_(g)on the composition, FIG. 50 shows the dependence of the crystallizationtemperature T_(x) on the composition, FIG. 51 shows the dependence ofthe temperature difference ΔT_(x) in a supercooled liquid on thecomposition, FIG. 52 shows the dependence of the melting point T_(m) onthe composition, FIG. 53 shows the dependence of the ratio T_(g)/T_(m)on the composition, and FIG. 54 shows the dependence of the Curietemperature T_(c) on the composition.

The saturation magnetization (σs) by VSM and the permeability (μe) andthe coercive force (Hc) by a BH loop tracer were measured for theamorphous soft-magnetic alloy tapes of EXAMPLES 7-15 to 7-18.

FIG. 55 shows the dependence of the saturation magnetization (σs) on thecomposition, FIG. 56 shows the dependence of the permeability (μe) onthe composition, and FIG. 57 shows the dependence of the coercive force(Hc) on the composition.

Figures attached to the plots in the ternary diagrams in FIGS. 49 to 57represent the glass transition temperature T_(g), the crystallizationtemperature T_(x), the temperature difference ΔT_(x) in the supercooledliquid, melting point T_(m), the ratio T_(g)/T_(m), the Curie pointT_(c), the saturation magnetization (σs), the permeability (μe), and thecoercive force (Hc).

In FIGS. 49 to 57, a figure shown in the vicinity of each isothermalline or isoline represents the temperature or the value thereof.

FIG. 49 illustrates that the glass transition temperature T_(g)increases with an increased total (PCBSi) content and a decreased Fe orAl content. The isothermal line at T_(g)=760 K lies along a line of thetotal (PCBSi) content y of approximately 21 atomic percent.

FIG. 50 illustrates the crystallization temperature T_(x) increases withan increased total (PCBSi) content and a decreased Fe or Al content, asin the T_(g). The isothermal line at T_(x)=800 K lies along a line ofthe (PCBSi) content y of approximately 21 atomic percent.

As shown in FIG. 51, the temperature difference ΔT_(x) increases with anincreased total (PCBSi) content and a decreased Fe or Al content. Theisothermal line at ΔT_(x)=35 K lies in the vicinity of a total (PCBSi)content y of 20 to 22 atomic percent and in the vicinity of an Fecontent of 75 to 78 atomic percent. Thus, the temperature differenceΔT_(x) in a supercooled liquid exceeds 35 K within the range of thetotal content y of 20 atomic percent or more and the Fe content of 78atomic percent or less. In particular, the amorphous soft-magnetic alloyFe₇₇Al₁(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))₂₂ of EXAMPLE 7-17 exhibits atemperature difference ΔT_(x) of 37 K

The temperature difference ΔT_(x) shown in FIG. 41 is larger than thatshown in FIG. 51. This difference is probably due to a difference in thecomposition between EXAMPLE 6 and EXAMPLE 7. The amorphous soft-magneticalloy shown in FIG. 41 has an Al content of 7 atomic percent, which ishigher than the Al content (1 to 5 percent) in the amorphoussoft-magnetic alloy shown in FIG. 51. Moreover, the amorphoussoft-magnetic alloy shown in FIG. 41 has an Fe content of 70 atomicpercent, which is lower than the Fe content (77 to 79 atomic percent) inthe amorphous soft-magnetic alloy shown in FIG. 51. Such differences inthe composition are considered to affect the temperature differenceΔT_(x). Thus, the temperature difference ΔT_(x) tends to increase withan increase in Al content and with a decrease in Fe content.

FIG. 52 illustrates that the melting point T_(m) exhibits the maximum of1,339 K at a higher-Fe-content side and the minimum of 1,282 K at alower-Fe-content side of the isothermal line at 1,300 K. Thus, thedifference between the maximum and the minimum is 57 K, which is smallerthan the difference 135 K in FIG. 42. Accordingly, the melting pointT_(m) of this amorphous soft-magnetic alloy is less sensitive to the Fecontent, compared to the B content.

With reference to FIG. 53, the sensitivity of the melting point T_(m) tothe composition affects the dependence of the ratio T_(g)/T_(m) on thecomposition. The ratio T_(g)/T_(m) slightly increases a lower-Fe-contentside of the isoline at T_(g)/T_(m)=0.58, which lies within the range ofFe content of 76 to 78 atomic percent. A large ratio T_(g)/T_(m) means adecreased temperature difference ΔT_(x) between the melting point T_(m)and the glass transition temperature T_(g). Thus, an alloy having acomposition within this range has enhanced amorphous formability eventhe cooling rate is decreased; that is, the critical cooling rate islow. Accordingly, the larger T_(g)/T_(m), the higher amorphousformability.

Comparing FIG. 53 with FIG. 51, the region of T_(g)/T_(m) of 0.58 inFIG. 53 overlaps with the region of ΔT_(x) of 35 K in FIG. 51. Thus, ahigh T_(g)/T_(m) region overlaps with a high ΔT_(x) region. Thus, thisamorphous soft-magnetic alloy has a temperature difference ΔT_(x) of atleast 35 K and exhibits enhanced amorphous formability by decreasing theFe content.

FIG. 54 illustrates that the Curie temperature T_(c) increases with anincreased total (PCBSi) content and a decreased Al content. FIG. 55illustrates that the saturation magnetization (σs) also increases withan increased total (PCBSi) content and a decreased Al content.

The Curie temperature T_(c) is highly correlated with the saturationmagnetization (σs). That is, the Curie temperature T_(c) and thesaturation magnetization (σs) increase by increasing the total (PCBSi)content and decreasing the Al content. Furthermore, the increased Curietemperature T_(c) contributes to improved thermal stability of magneticcharacteristics of the amorphous soft-magnetic alloy.

FIG. 56 illustrates that the permeability (μe) tends to increase as theFe or Al content decreases. Also, FIG. 56 illustrates a maximumpermeability (μe) of 27,000 at an Fe content of 77 atomic percent and anAl content of 3 atomic percent.

The permeabilities (μe) of EXAMPLES 7-16 AND 7-18 having the same total(PCBSi) content of 20 atomic percent are 27,000 and 19,000,respectively, which are significantly different from each other. Thus,it is considered that the dependence of the permeability (μe) on thetotal (PCBSi) content is not significant, as in FIG. 46.

FIG. 57 illustrates that the coercive force (Hc) tends to increase asthe Fe content increases and the total (PCBSi) content decreases. Thedifference in the coercive force is, however, small and does not show aclear dependence on the composition, unlike the above thermalproperties.

Accordingly, the thermal properties T_(g), T_(x), ΔT_(x), T_(m),T_(g)/T_(m), T_(c) show high dependence on the Fe and Al contents,whereas the magnetic characteristics including the saturationmagnetization (σs) does not show clear dependence.

Example 8

Manufacturing of Injection-Molding Article

Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B, and Siwere melt. The melt was injected into a mold shown in FIG. 1 to preparea toroidal injection-molding article (EXAMPLE 8-19) of an amorphoussoft-magnetic alloy as shown in FIG. 3. The resulting injection-moldingarticle had an outer diameter of 6 mm, an inner diameter of 4 mm, and athickness of 1 mm and had a composition ofFe₇₀Al₇P_(9.65)C_(3.45)B_(6.9)Si₃ which was the same as that in EXAMPLE6-4.

An injection-molding article of COMPARATIVE EXAMPLE 8-1 having an outerdiameter of 6 mm, an inner diameter of 4 mm, and a thickness of 1 mm andhaving a composition of Fe₇₀Al₅Ga₂P_(9.65)C_(5.75)B_(4.6)Si₃ wasproduced as in Example 8-19. This amorphous soft-magnetic alloy had thesame composition as that of the amorphous soft-magnetic alloy ofCOMPARATIVE

EXAMPLE 6.

The resulting injection-molding articles were subjected to X-raydiffractometry and DSC at a heating rate of 0.67 K/sec. The results areshown in FIGS. 25 and 26.

FIG. 58 illustrates that the injection-molding article of EXAMPLE 8-19has a broad X-ray diffraction pattern which is assigned to an amorphousphase. FIG. 59 illustrates that the DSC thermogram has a glasstransition temperature T_(g) at 760 K and a crystallization temperatureT_(x) at 822 K, thus the temperature difference ΔT_(x) in a supercooledliquid being 62 K.

As described above, the injection-molding article of EXAMPLE 8-19 has awide supercooled liquid region below the crystallization temperatureT_(x) regardless of the Ga-free composition and a large ΔT_(x)(=T_(x)−T_(g)) as a glassy alloy.

The injection-molding articles of EXAMPLE 8-19 and COMPARATIVE EXAMPLE8-2 were annealed at 698 K for 30 minutes. B-H curves of unannealedarticles and annealed articles were measured. The results are shown inFIG. 60 to 63. Moreover, the magnetic characteristics of these articlesare shown in Table 6 in which the magnetization B₈₀₀ indicates amagnetization in an external magnetic field of 800 A/m.

TABLE 6 Remanence Coercive Remanence Magnetization Magnetization ForceRatio Br (T) B₈₀₀ (T) Hc (A/m) Br/B₈₀₀ EXAMPLE 8-19 Unannealed 0.280.605 2.79 0.463 Annealed 0.38 0.990 1.83 0.384 COMPARATIVE Unannealed0.31 0.665 7.96 0.466 EXAMPLE 8-2 Annealed 0.02 0.995 4.00 0.020

FIGS. 60 and 61 show B-H curves of the unannealed and annealed articles,respectively, of EXAMPLE 8-19. FIGS. 60 and 61 and Table 6 demonstratethat the remanence magnetization (Br) and the magnetization (B₈₀₀) ofthe injection-molding article of EXAMPLE 8-19 increase by annealing,whereas the coercive force (Hc) decreases. Thus, the soft magneticcharacteristics are improved by annealing. It is considered that theinternal stress in the injection-molding article is relieved withoutprecipitation of a crystalline phase during annealing.

FIGS. 62 and 63 show B-H curves of the unannealed and annealed articles,respectively, of COMPARATIVE EXAMPLE 8-2. FIGS. 62 and 63 and Table 6demonstrate that the magnetization (B₈₀₀) of the injection-moldingarticle of COMPARATIVE EXAMPLE 8-2 increases by annealing, whereas theremanence magnetization (Br) significantly decreases and the coerciveforce (Hc) increases. Thus, the soft magnetic characteristics areimpaired by annealing. It is considered that a crystalline phaseprecipitates during annealing and the internal stress increases in theinjection-molding article, although no diffraction patterns suggestingan amorphous phase were observed by X-ray diffractometry of thisinjection molding article.

Although no crystalline phases are identified, the grounds for theassumption of the crystalline phase precipitation are as follows.

First, the amorphous soft-magnetic alloy of the injection-moldingarticle of COMPARATIVE EXAMPLE 8-2 is inferior in amorphous formabilityto the amorphous soft-magnetic alloy of the injection-molding article ofEXAMPLE 8-19. Thus, the regularity of the atomic arrangement in thetexture of the alloy of COMPARATIVE EXAMPLE 8-2 is higher than that ofEXAMPLE 8-19. As a result, a crystalline phase readily precipitatesduring annealing.

Second, it is considered that a slight amount of crystalline phase isformed or nuclei facilitating the crystal growth are formed due to lowamorphous formability of the amorphous soft-magnetic alloy ofCOMPARATIVE EXAMPLE 8-2 and crystallization from these nuclei occursduring annealing.

The reason that no crystalline phases are observed by X-raydiffractometry in COMPARATIVE EXAMPLE 8-2 is as follows. The crystallinephase precipitates into part of the texture and thus is not detected bythe X-ray diffractometry due to insufficient detection sensitivity.

As described above, the amorphous soft-magnetic alloy of the presentinvention exhibits high amorphous formability which facilitates theformation of a perfect amorphous phase by quenching an alloy melt. Thus,the internal stress occurring during the quenching process can berelieved without precipitation of a crystalline phase during annealing.As a result, the amorphous soft-magnetic alloy exhibits improved softmagnetic characteristics which are not achieved by conventional glassyalloys.

Since the amorphous soft-magnetic alloy of the present inventioncontains Fe as a magnetic element and Al, P, C, B, and Si havingamorphous formability, this alloy is primarily composed of an amorphousalloy and exhibits superior soft magnetic characteristics. Since Alenhances the amorphous formability, the entire texture can be composedof a perfect amorphous phase.

Since this amorphous soft-magnetic alloy has a large temperaturedifference ΔT_(x) of at least 20 K in a supercooled liquid, an amorphousphase can be formed from a melt at a relatively low cooling rate. Thus,a bulk alloy which is thicker than a tape can be produced. Inparticular, a bulk casting or injection molding article can be formed bya casting or injection process using a melt of an alloy.

This amorphous soft-magnetic alloy exhibits high amorphous formabilitycompared to the conventional Fe—Al—Ga—C—P—Si—B alloy. Since a perfectamorphous phase can be formed at a decreased cooling rate, a bulk alloyhaving a relatively large size and containing an amorphous phase can beproduced by a casting process.

Since the entire texture is composed of a complete amorphous phase, theamorphous soft-magnetic alloy exhibits significantly improvedpermeability and saturation magnetization, resulting in superior softmagnetic characteristics.

The internal stress in the amorphous soft-magnetic alloy can be relievedunder an appropriate condition without precipitation of a crystallinephase due to the complete amorphous phase, and the soft magneticcharacteristics are further improved.

1. An active filter comprising: a boosting converter circuit comprising:a switching element; a coil provided with a magnetic core generating aback electromotive force when the switching element breaks a DC current,wherein the magnetic core comprises molded article of a mixture of aglassy alloy powder and an insulating material, the glassy alloy powderhaving a texture primarily composed of an amorphous phase and exhibitinga temperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20° K. in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature; a rectifying element connected in seriesin the forward direction to the coil provided with the magnetic core forrectifying a current generated by the back electromotive force; and acapacitor for smoothing the rectified current; and a control unit forcontrolling the switching interval of the switching element of theboosting converter circuit.